Abstracts

The paper reconstructs when the Lagoon of Venice, Italy, was frozen over in the last 1400 years. The paper combines various proxies and instrumental readings, i.e.: written documentary sources since the origin of Venice; evidence from visual arts referring to 1709, 1789 and 1791 as well as some pictures taken in 1929 and 2012; finally, instrumental observations since 1716. A critical revision has been made of all sources in order to reject duplications or exaggerations introduced by late compilations. To this aim the various dating styles, the social and historical context of the city of Venice over time and the combined historical, statistical and climatological criteria necessary to validate data have been considered. The physics of ice formation, the influence of tides, the ice bearing capacity have been useful to interpret data. The passage from proxies to index and temperature in modern units is also discussed. The written sources provide basic information before the instrumental period and made possible a classification of winter severity. The visual arts provide a general view of what happened when the Lagoon was frozen over in the 18th century; in addition, they allow an estimate of the ice slab thickness. Visual arts, however, cannot be used for dating purposes. Finally, the instrumental readings are compared with the proxies in order to improve the interpretation of the above proxies. The result is a comprehensive, critically revised list of the harsh winters in Northern Italy and the meteorological situation responsible for their occurrence.

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This research has been made under the EU funded project Climate for Culture (Grant 226973).

The authors are grateful to Arch. Patrizia Schenal, Dr Laura Megna, Dr Mirca Sghedoni, Dr Leila Gentile, Dr Lorenza Mettifogo and Dr Luca Fraulini for their contribution in recovering and commenting documentary sources and to Dr Ruthy Gertwagen, Haifa University, and Dr Georges Pichard, Aix-Marseille University, for useful discussions and suggestions. Thanks are due to the three referees for the careful revision and useful comments.

1The Exarchate of Ravenna was a centre of Byzantine (East Roman) power in Italy, from the end of the (...)

2After the treatise of Campoformido, October 17th 1797, Venice and Milan were assigned to France. Na (...)

3The "kingdom" of the Lombardy and Venetian regions was formally instituted with the Congress of Vie (...)

4Treaty of Vienna, October 12th1866.

1The remote origin of Venice in the marshes of the Northern Adriatic Sea is related to local peoples that escaped from Germanic and Hun invasions in the 5th century A.D. and formed a community organized for mutual defence. In 751 the Duchy of Venice became independent from the exarchate of Ravenna1, and in 803 was recognized as Byzantine territory. At the end of the 9th century was a flourishing Republic, nicknamed “La Serenissima” (the Most Serene Republic). After the Fourth Crusade (1202-04) with the capture and sack of Constantinople, Venice became an imperial maritime power. In 1797 the invasion of the Napoleon Army determined the fall of the Venice Republic. In 1806 Venice become part of the Napoleon's Italian kingdom with Milan capital2, followed by the Austrian dominance of the Lombardy-Venetian regions (1814-1866)3. After popular unrests and battles, Venice joined the unified Reign of Italy in 18664. For its long history and maritime trades, Venice had special links with the Byzantine Empire and the Orient, but also strong relationships with other European countries, that influenced in various ways its activity and culture.

2In this paper we will combine various proxies and instrumental readings, i.e.: written documentary sources since the origin of Venice; evidence from visual arts referring to 1709, 1789 and 1791 as well as some pictures taken in 1929 and 2012; finally, instrumental observations since 1716. Of course, all documentary evidence provides insight into past climate conditions, but if separately considered, it can hardly be used to quantify climate change over time. However, taken together, proxy-data (ice cores, tree-rings, pollen, etc…) and historical documents tell us more than either could do alone. The result of this multidisciplinary effort will be a comprehensive, critically revised list of the harsh winters, with the indication of the winters that are often mentioned, but not justified.

3A reliable written source is a document that should be geographically and chronologically close to the facts, possibly written by an eyewitness. Documentary sources are extremely useful to reconstruct the past climate, especially for the period prior to the instrumental records. They provide data and details especially significant when cross-compared with natural proxies. They may include general descriptions useful to interpret the weather situation and the impact on environmental and society, what is not always possible with the instrumental readings alone.

5Enzi et al., 2013.

4However, some degree uncertainty is inevitable due to the cultural evolution and the change of interest to natural events5. For instance, in the Middle Ages the natural events were considered a direct sign of the Heaven, especially those occurring in the sky (that included the atmosphere), either to punish mankind or as an advertisement to change life style. In the Renaissance the natural events lost part of their religious significance and became lay and curious events to be collected and listed to amaze, improve erudition and knowledge. After the Galileo’s cultural revolution and especially in the times of Enlightens, they became object of study, an input for the scientific research. In addition, the cultural level of the eyewitness (and the author who collected and reported data) was crucial in determining the quality of the information. The survival of a memory is linked to the perception of its importance, both for public and private reasons. This perception changes depending on the cultural atmosphere the authors is part of. Therefore, literary sources evolve differently in quantity, quality and typology over time. It is essential to keep in mind this evolution in order to interpret data and assess the correct uncertainty band, as we will discuss later.

7The State Archive was founded in 1815 with the name: Archivio Generale Veneto (i.e. General Archive (...)

5Venetian documents provide a unique opportunity for reconstructing a long series of extreme events that have characterized the past climate over one millennium.6 Our research has been conducted in Venice and outside Venice as well. In Venice, historical documents are kept in the Marciana Library, Correr Museum, Querini Stampalia Foundation, State Archive and other public and private collections. In particular, the State Archive was founded in 18157 to reorganize collections and reconstruct the history of Venice: it preserves documents for about 80 km of shelves. The records are written in Latin, Venetian, early and modern Italian and include official, public and private documents of the central and local institutions, local and foreign political and administrative records, diplomatic and informative letters from foreign embassies, ship logs, professional and artisan guild records, notary archives, brotherhoods, associations and confraternal archives. The documents provide descriptions of weather events and their impact on the society, the agriculture and the landscape. Interpreting these data allows determining the level of severity of the events that happened before the instrumental observations of air temperature, pressure and precipitation.

6The Digital Humanities Laboratory (DHLAB), founded in 2012 by Frédéric Kaplan, is developing new computational approaches for document digitalisation, under the ‘Venice Time Machine’ project, jointly supported by the Ecole Polytécnique Féderale de Lausanne and the University of Ca’ Foscari, Venice8. The aim is the digitalization of millions of documents over the last one thousand years; the project will make much easier the research in digital form. Another useful digital source is HISTRONE-CEREGE9 with hydrological and climatic data with special reference to the basin of the Rône River.

7In the Middle Ages the information was rare, especially in the dark period before 1100. The population was scarce, lived in very bad conditions and was unable to read and write, except a few persons, mostly clergy. In times in which it was difficult to survive, the interest to document weather and climate was very low. In addition, the few documents that were produced were not kept in the best conditions, and not all of them survived fires, floods, wars, dismantlement and other challenges. Possible information gaps are due to dramatic fires occurred in Venice, especially in 976, 1105, 1149. A question is whether the period from 853 to 1119 is a gap for scarcity of documents, or passed unobserved being characterized by normal or mild winters as a result of the Warm Medieval Optimum? Our research confirms the former hypothesis, while the second remains obscure.

10Von Oppolzer, 1887.

11Camuffo and Sturaro, 2004.

8A general problem is that the recovered series of data should be complete, because a missed winter may be misinterpreted for a “normal” winter that was neglected because it had no particular features. The problem is that the number of events per each class in unknown. As an exercise to test completeness of a series and at the same time have a general view how the cultural approach changed over time is given in Fig.1, that compares the completeness of our data bank as it was some ten years ago, after some thirty years of traditional documentary research in archives and libraries, before the digitalisation of many historical documents was available with rapid improvement of the stuff. We should explain that in our Data Bank, in addition to weather events and natural challenges, we reported the solar and lunar eclipses that we have found in the documents because they were precious to exactly date the weather events happened in the same period. The underlying idea is that we exactly know the real number of astronomical events (AERN), e.g. comets, eclipses, which are calculated with astronomical formulae10, and we can compare this number with the same type of events recovered in our data bank (AEDB). At this point we can compute the completeness in terms of percentage11, i.e. [(AERN)/(AEDB)] ×100. The total number of primary (i.e. direct eyewitness) and secondary (i.e. reported by another writer) sources is also reported in the same figure.

Upper row: Percentage of the number of solar and lunar eclipses recovered with other natural events in our Data Bank (year 2000) in comparison with the total number of eclipses occurred in the same period (i.e. century by century), and known after astronomical calculations. Lower row: Number of primary and secondary sources that have been consulted. For symbols A, B, C, see comments in the text.

9The number of available and consulted sources and the percentage of the eclipses (as an index of completeness) over time are reported in the plot. In the first millennium of our era (label A) the number of sources is very low and is associated with a very low percentage of eclipses. This means that the information is largely incomplete. In the upper row, in the period B from 1000 to 1400 the percentage of eclipses is very high (around 70%) especially considering that the sky is naturally overcast with thick cloud cover at least for 30% of the time. In this period the “sky” was composed of a unique complex system of spheres including stars, planets and the atmosphere. In the upper row we see an abrupt transition to C, that is due to cultural factors: after the discoveries of Nicolaus Copernicus, Tycho Brahe, Johannes Kepler and Galileo Galilei, the eclipses became natural celestial phenomena studied by astronomy and were distinguished from the weather events in the atmosphere. In our Data Bank (Fig.1 lower row) the passage from B to C corresponds to the reduced need of documentary data, substituted by instrumental readings, except for a common period necessary for the calibration and validation of the series. This examples elucidates how dark and incomplete is the first Millennium, and suggests prudence in drawing climatic conclusions only relying on documentary sources.

12The Convention for the restitution of stolen artworks and documents was held in Florence, July 14th(...)

10The next severe challenge to the documents in Venice happened in 1797, when the Napoleon Army determined the fall of the Venice Republic and dispersed most documents, although some of them were given off in 1869 after the Austria-Italy Convention12.

11In some cases the content of certain documents survived because they had been copied into chronicles or compilations. For instance, the German book dealer Amadeus Gottlieb Schweyer living in Venice and locally named Amedeo Svajer, collected thousands of manuscripts and books of social and political interest for Venice, including plagues, extreme weather and natural disasters. This was an unparalleled collection about the history of Venice. When Svajer died in 1791, his brothers decided to sell the collection, which was dismembered 13. The Inquisition of the Venice Republic controlled the collection, found 900 confidential documents and confiscated the most critical ones (some 252 diplomatic letters and reports to and from foreign embassies) in a special archive of the political Court. Most books were bought by the bookseller Scapin in Padua; 721 manuscripts were bought by the Civic Library Joppi, Udine; 340 codices were purchased by the Marciana Library, others by the Museum Correr; the 252 diplomatic documents passed to the State Archive; the books and documents given off by Austria in 186914 were dismembered in various archives. The rest of the Svajer’s collection was scattered over Europe. However, when Svajer was alive, the local chronicler Father Giovan Battista Gallicciolli consulted per years the collection, as well as other public and private archives and libraries in Venice to compile a holistic chronicle of Venice published with the title “Delle memorie venete antiche profane ed ecclesiastiche” (early secular and ecclesiastic Venetian memoirs) (Gallicciolli, 1795)15. Except for the title, this text is almost identical to another anonymous manuscript “Cronaca Veneziana o meglio Zibaldone con molti ricordi meteorologici” (Venetian Chronicle or Hotchpotch with several weather memories), kept in the library of Correr Museum. We believe that the anonymous manuscript is the draft of the publication by Gallicciolli printed in 1795. In the following, will quote only Gallicciolli 1795, disregarding the parallel handwritten Hotchpotch. Gallicciolli accurately copied representative fragments of the original documents and shortly reported the source in contracted form, or the archival number of the collection, either the Svajer’s or other ones. Although weakly quoted, Gallicciolli preserved many useful fragments of unusual or extreme weather events of which the original source has been dispersed or lost. In this paper, the documents of the Svajer’s collection that have been found in other archives or libraries have been quoted according their modern classification. Some other of these documents might have survived, but so far it has not been possible to find them. The lost documents have been cited with their original quotation, e.g. Svajer No 421 and No 865. Gallicciolli was very accurate for his time, although in some cases he misled dating and caused duplications of events for the reasons we will discuss later. Gallicciolli was a source directly or indirectly used by a number of climatologists specifically interested to Venice,16 or Europe in general 17, generating the problems we will discuss later. Gallicciolli followed the example of other famous catalogues, as follows.

12Julius Obsequens, a Roman writer of the 4th century A.D., wrote the Liber de Prodigiis (Book of Prodigies) including the wonders and portents that occurred in Rome from 249 B.C. to 12 B.C.18 The book was edited and printed by Aldo Manuzio in Venice in 1508.

13On request of his friend George Syncellus, the Byzantine monk Theophanes the Confessor continued the Syncellus’s Chronicle “Chronographia” a chronology of world events, covering the period from the rule of Diocletian in A.D. 284 to the downfall of Michael I Rhangabes in 813. The Chronicle was written in Greek, and dated in years since the Creation of the World.

19Fritsche 1555.

20Tho Hexapolis exist. The Doric Hexapolis was a federation of Greek city-states in South-Western Asi (...)

21Fritsche 1555.

14In 1555, Markus Fritsche19 (who signed MarcusFrytschius Laubanus) of Greek origin, i.e. "Hexapolensis"20 as he defined himself, in the middle of the 16th century, published in Nurnberg, Germany, a book written in Latin, i.e. the “Catalogus Prodigiorum” (Book of Prodigies, where "prodigies" stays for: extraordinary, upsetting things)21. The book is an extensive catalogue of the most impressive meteorological and celestial events, ordered year by year, since the Creation of the World. He used double dating. In the B.C. era he used as a reference the Creation and the foundation of Rome; in the A.D. era he used the Creation and the years of Christ. He quoted in abbreviated form his sources. Some of them are understandable, other remain obscure. Fritsche was used as a (secondary) source by leading historians of climate in the next centuries.

22Calvisius 1605, 1629, 1685.

15In 1605, Sethus Calvisius, a German musician as well as chronologist and astronomer, published the book “Opus Chronologicum” later updated to 1629 by J. Zhym and to 1685 by Wolfgang Philipp Kilian22. Clavisius reported a detailed list of the main political and social events, including natural hazards and extreme climatic events since the antiquity, dating the facts in year after the Creation and relating them to the Common Era as well. Calvisius included several facts concerning Venice and was considered a milestone reference.

16A key reference was Father Secondo Lancillotti who published in Venice in 1627 a comparison between the situation at his time and how it was in the past under various aspects: e.g. ethical, social and catastrophic including plagues and natural hazards. The short name of the book (in Italian) is “Hoggidì” (i.e. Today). The events are listed with the year as heading on the side, and the source is mentioned but much shortened: some may be guessed and found after various attempts, other remain obscure. The book is written in Italian and was a main reference for Giuseppe Toaldo, but not for other scientists unfamiliar with Italian. However, Toaldo wrote in Italian, Latin and French and was translated in German and English. This allowed the transmission of most events quoted by Lancillotti, but the official source became Toaldo.

23Toaldo in 1770, 1781,1797.

24Camuffo 1987, Camuffo and Enzi 1992a, Enzi and Camuffo 1995.

17Another catalogue of meteorological events including harsh winters was made by Giuseppe Toaldo in 1770, and particularly in the 2nd edition in 1781 and the last update in 1797.23 Toaldo was a famous and excellent astronomer and meteorologist living in Padua, located 40 km West of Venice, and his papers had a wide diffusion over Europe. From 1766 he performed records of instrumental observations and tried to find how far astronomic factors influenced weather. For this purpose he collected a huge amount of data and events from any available source, either direct witnessed or second-hand compilations. He acknowledges that, in general, his main sources were “Fryschio” (i.e. Marcus Fritsche), “P. Lancillotto” (i.e. “P.” for “Father” Secondo Lancillotti) and “Collezione Acad. T. IV”. Probably, he intended the Collection l’Académique published at intervals of a few years at Dijon andParis; this journal included summaries and articles of foreign works translated in French. The fourth Tome (i.e. T. IV) was focused on natural history, botanic, physical and chemical advances, medicine and anatomy. Toaldo consulted various issues searching for news of extreme meteorological events and other natural hazards. His aim was to build a database of meteorological events to be related to astronomical cycles. In his works, Toaldo only seldom reported the source in a very abbreviated form; he did not seek for the original documents and accepted the items available in compilations without verifying the content or checking dates. This generated some errors and duplications that were transmitted to later historians of climate, as discussed elsewhere.24 However, for the astronomical or meteorological observations he made, and for the contemporary period of which he was a witness, Toaldo is absolutely reliable. Toaldo could not take advantage of the Gallicciolli’s book because it was published in 1795, two years before Toaldo died.

18Several other studies were made on harsh winters, although not focused on Venice. In the following we will quote some of them to help interpreting the transmission of data and possible duplications of events.

25Pilgram 1788.

26Tilloch, 1820, Arago 1858, Hennig 1904, Easton 1928.

19In 1788, Anton Pilgram, an early climate historian and statistician from the University of Vienna made a very careful collection and statistical analysis of weather events from the existing literature and published it (in German) with a list of the winters in the common Era (more exactly since A.D. 401), with a comment on their severity25. He quoted (but not controlled) all sources, either primary or secondary ones, including compilations (e.g. Lancellotti, Toaldo). The work has a modern approach and inspired later works: certainly Tilloch, but very likely Arago, Hennig and Easton26 too; the latters preferred to mention the original source, omitting to quote Pilgram.

27Pfaff 1809.

20In 1809, Christoph Heinrich Pfaff from Kiel published (in German) a description of the harsh winters since A.D. 140027 with a few mentions to some previous exceptional winters, e.g. 1269, 1323. He relied on four papers, published from 1753 to 1800, mostly dealing with winters occurred on the previous century. This work was used by Tilloch and others therein.

28Tilloch 1820.

29Le Roy Ladurie 1983.

21In 1820, Alexander Tilloch, editor of The Philosophical Magazine and Journal, published the History of the Weather where he reported a list (in English) of all major weather events occurred in the Christian era, including the harshest winters. As Toaldo, he did not mention and control his sources, except in the introduction where he declared that relied on Toaldo, Pilgram and Pfaff. It is quite surprising that Tilloch accepted without a critical revision the above contributions because in the foreword he made excellent and prudent introductory remarks, i.e.: “'Prior to the instrumental period, we must glean our information from the loose and scanty notices which are scattered through the old chronicles relative to the state of the harvest, the quality of the vintage, or the endurance of frost and snow in the winter. Great allowance, however, should be made for the spirit of exaggeration and the love of the marvellous; which infect all those rude historical monuments.”28 By the way, Tilloch anticipated by one and half century the idea of Emmanuel Le Roy Ladurie to reconstruct the spring-summer temperature in Borgogne from grape harvest dates. 29 The list of weather events by Tilloch was a very useful source for later chroniclers and historians of climate, and caused several duplications too. A number of events concerning Italy were not confirmed by our local contemporary sources. In general we will disregard this, and other late compilations, except for discussing the reliability of some winters, especially in the 17th century.

22In 1821, Gabriel Peignot wrote (in French) a paper with a detailed list of the harshest winters from 396 BC to 1821, with a short description of the most impressive events. The sources were quoted, but not always.

30Arago 1858.

23In 1858 François Jean Dominique Arago30 with the cooperation of J.A. Barral published (in French) a huge stuff of climatic data, including a Chapter devoted to the winters when the great Rivers were frozen. He reported the text (translated in French) and the sources, all of them supposed to be accurate and reliable. This work was very popular and became a useful reference for historians of climate.

31Hennig 1904.

24In 1904 Rudolf Henning31 published (in German) a very extensive catalogue of remarkable weather events indicating the sources but without a critical evaluation of them. This work was a milestone reference.

32Easton 1928.

25In 1928 Cornelius Easton32 published a catalogue listing all winters in Western Europe, quoting the sources. Each winter is introduced with keywords or a short sentence that summarizes the various sources. The book is in French, but several quotations are in the original language, and this is very useful for a better evaluation of the original text. No comments are reported about the sources. This also was a milestone reference.

26In the second half of the 20th century, the reconstruction of the past climate became a mature science with collection and revision of historic data and sources interpreted in terms of weather or climate analysis. Pioneers have been Hubert Lamb in UK, Emmanuel Le Roy Ladurie in France, Christian Pfister in Switzerland, Gaston Demarée and Pierre Alexandre in Belgium, Rudolf Brazdil in the Check Republic and many others.

27A totally different source of information that we will use in this paper is constituted of visual arts that illustrate what we find in written documents. These visual arts are kept in a number of institutions, i.e. Foundation of Civic Museum (MUVE, Venice, that includes Ca’ Rezzonico and Correr Museum cited in this paper), the Querini-Stampalia Foundation, private collections in London.33 In addition, some interesting pictures exist, documenting the Lagoon frozen in 1929 and more recently as well.

28Meteorological records of daily temperature observations that started in 1716 in the Venice area, including Padua, are another vital source of information.34 We have recovered, corrected and analyzed all the related instrumental records.35 Padua was rich of scientific observations, because the local University, founded in 1222, was interested in all disciplines, with leading teachers. Giovanni Poleni in 1719 had a chair in Mathematics and Experimental Philosophy, and then Astronomy Mathematics and Navigation, and began daily weather observations in 1716. Giuseppe Toaldo in 1764 had a chair in Astronomy and Meteorology and in 1766, after the death of Poleni, continued the series of meteorological observations including detailed descriptions of weather extremes. This long instrumental series has been continued till today.36

29We have also consulted the weather readings of the Patriarcale Observatory, Venice, that are reported in form of Daily Logs with notes. This Observatory is located in the City centre and was active from 1835 to 1951. After it was closed, the nearby Istituto Cavanis continued the readings since 1959.

30A further source of instrumental readings from 1950 is the Italian Air Force Weather Service at the Venice airport on the border of the Lagoon. The records of the instrumentalperiod allow to reconstruct the weather maps and the general circulation.

31In Venice dating was complex and sometimes ambiguous due to the use of a number of different styles that co-existed until the fall of the Serenissima in 1797. The various dating styles are37:

“More Veneto” (i.e. Venice Style) calendar with the year beginning on March 1st. This is the most official and popular style of the Republic till 1797.

38The Julian Calendar introduced by Julius Caesar in 46 BC was the predominant calendar in the Roman (...)

39Cappelli 1983.

"Circumcision of Christ" or "More Romano" (i.e. Rome Style) calendar beginning on January 1st, as the modern style. It may be indicated A.D. i.e. anno Domini, Latin for “in the year of our Lord.” From the origin of Venice to October 4th 1582 it coincided with the Julian calendar; after October 15th 1582 with the Gregorian calendar38. Since 1520 it was sometimes used in private acts. Before 1797 it was used for official documents sent to foreign people not familiar with the More Veneto.It became the official style after 1797.39

“Byzantine” calendar: from September 1st, anticipated by 4 months. This was the official calendar of the Byzantine Empire from 988 to 1453 i.e. the fall of Constantinople and the end of the Byzantine Empire, followed by the Ottoman Empire (1453-1922). This style used the “Annus Mundi” or “Ab Origine Mundi” (AM, Latin for “Year after the Creation”) that was established 5,509 years before the Incarnation of Jesus Christ.

“Constantine Indiction” or “Caesar Indiction”, or "Beda Indiction" or shortened "lndiction", after the emperor Constantine, based on the taxation date, starting from September 24th. Each Indiction was composed of a series of 15 years that were numbered from 1 to 15, returning to 1 at the next Indiction. It was used in the early period of the Republic when the link with the Byzantine Empire (330-1453) was strong. Critical dates were: 1204 when Venetians and the crusaders of the IV crusade captured and sacked Constantinople; 1453 with the fall of Constantinople.

“Constantinople Indiction”, or “Greek Indiction” or shortened "lndiction", based on taxation date, from September 1st. This style was in use in the early period of the Republic, during the Byzantine Empire.

“Roman Indiction” or “Pontifical Indiction” or shortened "Indiction", fromDecember 25th. This was used in the last period of the Republic, when the Byzantine Empire was ended, substituted by the Ottoman Empire.

"Hagiographic calendar”, a monastic use where each day of the calendar year is linked to an individual Saint. This style was particularly popular in the Byzantine area, with calendar-icons composed of 365 Saints. This calendar does not establish the year but the day and month.

“From the Rise to Power” of the Doge. The Doge was elected for life by the Venice aristocracy and was the chief magistrate of the Republic, with great temporal power. This dating style indicated the year of power of each Doge, and was an ambiguous substitute of the year because the start was random, and the same year Doge style was spread over two years More Romano. Fortunately, the chronology of all Doges is well documented.

“Closest Milestone”, i.e. making reference to some famous natural or social events used as a milestone, e.g. passage of a comet, eclipses, famine, earthquake, battle, death of a king. This dating style was particularly popular in the antiquity and the Middle Age. The use was to quote the closest among the possible temporal references that had a special social or psychological impact. A problem is that the reference event may have occurred before or even after the particular event the author was dealing with.

32Other additional calendars were used in documents referring to Venice but written in other Italian cities. The use changed with the cities and over time, following political events. The most important dating styles were:

“Easter”: from the Easter Day.

“Incarnation”, Florence style, used in Florence, Piacenza and other cities: from the 25th March postponed by 84 days compared to the Julian and Gregorian calendars A.D., i.e. More Romano (beginning on January 1st).

“Incarnation” Pisa style, used in Pisa: ended March 24th, anticipated by 281 days.

33The main problem is that the dates are almost always reported without specifying the dating style, Indiction type etc. For the local writer the choice was obvious and no specification was needed. However, after a long time has passed, this created ambiguity or misunderstanding. For instance, an event happened on January 1500 (in terms of the Julian calendar) was dated: 1499 if the writer used the Pisa Incarnation style; 1500 if used More Romano or Nativity or AD; 1501 if used More Veneto, Easter or Florentine Incarnation. This example shows that a date may have an uncertainty of ±2 years. The situation is particularly critical for the winter severity, as the extreme cold is usually reached in December, January or February that may belong to the same or the next year, depending on the particular calendar used. This complex and misleading system explains why some dating remains uncertain, or created duplications, especially for the mediaeval period. All the dates reported in this paper will follow the modern style, except when quotations are used. The analysed sources show that the most frequent period for the Lagoon to freeze over is from January to February and, only very rarely, in December. Therefore, when no specification of the month is found, the most probable assumption is that the winter date is related to January or February.

34Another consequence of the complex dating styles, or the use of secondary sources (i.e. not direct witness) is the single (or multiple) duplication of events. In particular, most historians of climate since the beginning of the 20th century omitted to mention how they knew the fact, making almost impossible to verify the source. For this reason, a critical analysis of the text is necessary, based on the optimization of three criteria: climatic, statistical and historical, as follows

35From the climatic point of view, it is evident that some dates are wrong. For instance, suppose to find a great winter (GW) mentioned in a manuscript but not in others dealing with the same time period. A great winter cannot be local and should be perceived by all people of a wide geographic area. It is not physically realistic that a certain winter is considered GW by a source and normal by another. Finally, the various effects described in the text should be physically consistent.

36From the statistical point of view the probability that an extreme event returns in the next year is extremely low. A great winter generally occurs twice or three times per century. Suppose the case of a century with two GWs. The probability that a GW falls in a selected year is 0.02, but the combined probability that in the second GW falls in the next year is about 100 time smaller40. As human errors in the transmission of the date (especially for secondary sources) have a much higher probability, when extreme events are found in two consecutive years they should be considered suspect, and a careful analysis is required.

37From the historical point of view, the simultaneous existence of various and undeclared dating styles, misprints or errors in reading, interpreting or copying previous documents, may cause misleading dates or duplications of events. The most favourable case is when the text reports some astronomical events (e.g. eclipses or passage of comets) that can be verified with astronomic calculations, as we did it. Internal controls are possible: if a specific day of the week is mentioned in addition to the date, name of the day and date should match for the specified year; if not, another year should found in which they match. To reject an event because the source has not been well identified means to deny that this event had occurred, and this may constitute a serious error in the climate reconstruction. A weak source means to start a long hardworking to verify or to deny the obscure event.

38Briefly, two extreme winters at short distance between them are credible only in the case they have been recorded in the same source, contemporary to the events. When they derive combining two or more sources that mention only one of the two winters, almost certainly one of the two is a false duplicate. Extreme events mentioned in different sources, but differently dated, need an accurate critical analysis to establish the most probable dating. In past climate reconstructions, it is unavoidable that some events may remain obscured by uncertainties. In the case of doubt, this should be notified; after, the key question is: to accept or to reject? Which of the two options may cause the greatest possible error in the climate reconstruction?

41Proxy data are natural or man-made indicators that preserved physical characteristics of the enviro (...)

39When we have instrumental records, the winter severity is evaluated from the temperature level reached during the winter, and the time duration in which the temperature was below certain selected thresholds. In the period before the instrumental records, however, we must rely on proxy data41, also called proxies. Historical documents and visual arts contemporary to the events are useful proxies, because they contain a wealth of information about past the climate and the ice sheet. The interpretation of the above proxies is based on the effects generated by cold. It is possible to establish a class of severity, based on some specific objective consequences, easily recognizable in the historical documentation. In this paper, the winter severity has been classified in four categories, from the mild to the coldest, i.e.: mild, normal, severe, very severe and great winter.

40“Mild” winter was considered warmer than usual, without frost events, and with early vegetation. In a mild winter a modest use of wood for domestic heating was required. No ice is formed on the Venice Lagoon.

41“Normal” meant average or passed unobserved, without comments about its severity or its ramifications on the society and economy. No ice is formed on the Venice Lagoon.

42Siltation is the fine particulate terrestrial clastic material transported in suspension by the tur (...)

43Mangiarotti, 1814.

44Daily Logs of the Patriarcale Observatory, Venice.

42“Severe” winter (SW) was identified according to the many complaints made by a number of separate sources. A winter is considered severe if the intense cold persisted for a short period with frost, but large water bodies were not completely frozen over. In Venice, ice slabs formed inlands on the freshwater of rivers or on the borders of the Lagoon, where shallow water lasted for a long time without exchanges with the sea. Often the Lagoon birds who used to nest there were entrapped with their legs in the ice. Discharged from rivers, the ice slabs that arrived into the Lagoon were hardly visible and formed icebergs that endangered the small Venetian boats. This was one of the reasons Venice initiated the diversion of the main rivers outside the Lagoon; the main reason, however, was to clean the Lagoon from fluvial siltation42. Two examples of SW are reported. The first, "On February 22nd 1814, there was cold with fresh wind. On the 23rd, ice was floating on canals. On the 24th, fresh wind transported slabs of ice. The navigation was dangerous and was stopped"; the temperature was -6°C.43 The second case was “On January 29th, 1855; some slabs of broken ice were floating in the Lagoon. Several canals between Venice and the mainland froze and prevented navigation. There were also some casualties. The edges of the canals in Venice were covered with ice. On the morning of the 21st [with minimum air temperature -8.8°C] many slabs of ice were floating on the Grand Canal, arriving from the canals between Venice and mainland. On the 24th too some ice was still floating".44

45Cavanis, 1788.

43“Very severe” (VS) winter was thus classified when the cold killed people, animals and plants and caused to the complete freezing of springs, wells and large bodies of fresh water. The Lagoon around Venice, characterized by shallow waters and smaller water exchange, partially froze, and the deep canals crossing the City, characterized by larger water exchange, were covered with ice slabs. Furthermore, the ice made impossible the import of food and beverages from the hinterland and caused to the City to be besieged by the cold. Theoretically, the only possibility to get new supplies was by the sea. However, internal shipping was extremely dangerous, not only due to floating slabs, but because most ships were entrapped in the ice, and it was impossible to reach and save them. In the case of very severe winters the Venice Republic provided the poor people with leftover wood from the public shipbuilding industry, the Arsenal, for heating and cooking purposes, for their survival.45

46The freezing point of wine depends on its alcohol content. A common wine in Northern Italy (9 to 13 (...)

44“Great winters” (GW) are extreme exceptional events that generally happened once in a century. The extreme cold lasted for weeks, killing people, animals and trees. The wine in barrels46 and the water in all springs and wells froze, as in the VS winter. In addition, large bodies of water were covered with thick ices slabs that could carry heavy weights. At a certain point the thick ice sheet in the North-Eastern side of the Lagoon from Venice to Mestre in the hinterland, along the sides of St. Michael and Murano islands (Fig.2), supported the weight of people, animals, barrels, carts and even wagons.

Path over the frozen Lagoon frozen from Fondamenta San Giobbe in Venice to Mestre in the hinterland, through S. Secondo Island (yellow arrow); the second path is from the Fondamenta Nuove passing on the side of Saint Michael Island and across Murano Island (red arrow).

Arrows have been applied to a xylography by Jacopo De’ Barbari (16th century, Correr Museum) with a realistic aerial view of Venice and its Lagoon. Correr Museum, Venice, inv. Cl XLIV n. 57)

47Cotte, 1790.

45A new pathway was thus created that raised the siege off the City. This situation is illustrated by a funny xylography (Fig.3), whose legend in the bottom reads: “Activities made on ice 1st January 1789 and a pulled cart with poultry and mail”. Furthermore the thick ice created new vast areas for people amusements and games exhibited by this xylography, paints and etchings, discussed later. A similar situation with analogous effects took place in Europe. In France, eight months after the event, Father Louis Cotte reported that the severe frost of the great winter 1788-89 killed animals (e.g. hens and turkeys loft their legs sucked in ice; fish in shallow waters), fruit and forest trees and other vegetables (including winter barley, corn and wheat). The frozen water did not enable grinding wheat.47 Furthermore, the frozen fresh water hampered the transport of supplies from the countries nearby, leaving French people without bread and in the famine. This situation, bad climate and food shortage accelerated the onset of the French revolution.

46The Venice Lagoon has a surface area of around 550 km2 and, although it is only one water body, for the internal circulation it may be considered composed of three parts: Eastern, Northern and Western, each of them with its own gate to the Adriatic Sea. When Venetians use the term Lagoons, it means that all the three parts are considered; the singular term, Lagoon, means either the whole Lagoon or one of the three parts, depending on the context. The common use by modern documents is the singular term. The documents considered in this paper define "marshes" the shoal areas, either with shallow water or no water at all, depending on the tidal phase. The Lagoon water is generally shallow, but some deep canals cross it to allow the transit of boats and to reach the Sea. The City of Venice is a cluster of small islands carved out of a swamp: they are joined together by bridges and crossed by canals. Shallow waters and deep waters respond in a different way to local water circulation and frost, as we will discuss later. In this paper we will limit our analysis to the harshest winters in Venice, that is, the VS and GW when not only the marshes, but the wide and deep canals too were frozen.

47When historical documents are cross compared to verify their agreement and assess the winter severity, one might expect to find that the Venice Lagoon is in the same conditions as the lakes and rivers of Northern Italy, i.e. either covered or uncovered by ice. However, it is necessary to keep in mind that the physical situation of a Lagoon is different from lakes and rivers for three reasons, as follows.

48Camuffo 1987.

48(i) Water composition. The most obvious difference is that the Lagoon is composed of salty marine water, while lakes and rivers of fresh water. The marine water has a salt content of about 3.5%, which lowers the freezing point to about -2°C. Before the works made by Venetians to divert the rivers outside of the Lagoon48, i.e. 14th to 18th century, the salinity in the Lagoon was a bit less and so the freezing point. The contribution of rainfall to salinity is negligible because the winter precipitation in this area is 50-60 mm/month, but the weather situation responsible for icing is characterized by extremely cold and dry air blowing from North and no precipitation for the whole period. Ice that forms from freezing seawater is composed of a regular crystalline structure where salt cannot be included. This means that marine water freezes when the temperature drops below -2°C but will melt when it exceeds 0°C. Freezing and melting occur at different temperatures, differently for the fresh water of lakes and rivers that freezes and melts at 0°C.

49When a thick cloud cover is present, it intercepts and returns back a large part of the IR radiatio (...)

50The solar income is the amount of solar energy that falls on a surface (e.g. the Lagoon) as sunligh (...)

51Garcic et al. 1997.

52The largest tidal cycles occur when the Earth, the Sun and the Moon are in conjunction (new Moon) o (...)

49(ii) Heat balance and tides. In winter, any water body looses heat towards the atmosphere (by evaporation, intense infrared loss when the sky is clear49, heat conduction and wind convection) and uptakes some heat from the bottom and the solar income50. The above balance determines the water temperature: in winter the shallow water of the Lagoon is cold while the Adriatic Sea is warmer, e.g. 8-10°C51. However, at each tide the Lagoon has an exchange of water -and heat- with the Adriatic Sea, and the tidal cycle is governed by the lunar phases. At the first and last quarter Moons, the tidal range and the water exchanges with the sea are minimum; at new or full Moons are maximum.52. This particular synergism of lunar and solar forces brings inside the Lagoon smaller or larger amounts of mild seawater that opposes the formation of ice, or tends to melt the ice sheet from below. In order to be frozen over, the Lagoon should be exposed to extremely cold wind for a certain period, e.g. one or two weeks. Lakes and rivers too may freeze under the same conditions. However, differently from the Lagoon, they respond to the cumulative effect53 of continuous cooling over a long time (e.g. months) although the cold is less intense. For lakes and rivers the water temperature depends on the total heat lost, either short-term intense cooling or long-term moderate cooling. This justifies why at times the Lagoon, lakes and rivers in the same climatic area are simultaneously frozen over, while other times only lakes and rivers are covered with ice.

50(iii) Capability of accumulating ice slabs. Rivers may transport slabs of ice formed near the borders and the slabs of ice may be stopped at bridges or meanders, where they will join together. When a number of ice slabs accumulate on the same restricted area, they may join together forming a very thick slab acting as a bridge, while the rest of the river remains unfrozen. The Lagoon too may have ice floe areas, especially near the borders or transported by rivers or inland canals, but this is of little relevance. When floating ice slabs are enough, they will collide with each other and might join together expanding the frozen area. The further development of ice is conditioned by the balance between tidal exchange and further atmospheric cooling for cold air, strong wind and clear sky for infrared cooling. In other words, when the Lagoon is frozen over, it is very likely to find lakes and rivers frozen too; the vice-versa is not necessarily true.

51The Lagoon has a short relaxation period determined by exchanges with the open sea, and the critical factor for freezing is that the intense cooling should exceed the heat supplied from the sea at each tidal cycle. Thick ice slabs form on the Lagoon when the air temperature drops below -10° to -18°C for one or two weeks or even for longer. The most effective mechanism for the Lagoon to freeze is snow followed by polar air blowing from North, locally resulting in strong Bora wind from North-East. When snow covers the soil, the air in contact with it never exceeds 0°C; the Bora increases evaporation from the water surface and further cooling.

52The Lagoon has shallow waters and some canals as well, and we have seen that the water temperature mostly depends on the tidal exchanges with the sea. Ice is thicker on borders and marshes, but thinner or even missing on the canals. To the expert eye of local people, in the absence of frost, the canals are recognizable from the different refraction of the waves, but this is not possible when there is an ice cover. However, the main canals are marked with poles implanted on the canal borders. When both the Lagoon and the canals are covered with ice, the ice on the canals is thinner and the poles indicate the most risky areas where some mild water flows below for tidal exchanges.

53It is hazardous to walk on ice when its thickness is less than 10 cm. The ice sheet is safe for the weight of individual persons when the thickness exceeds 18-20 cm throughout the entire area.

54Department of Transportation 2007.

54The threshold for ice-bearing capacity (Fig.4) is given by the Gold’s formula L = 4x2, where L is the load limit in kg and x the ice thickness in cm.54 The safe area is on the right, far from the threshold, and is affected by a number of factors in addition to the ice thickness. The risk factors include the pressure of water below the ice sheet, cracks, tidal cycles and related exchanges with milder seawater, sudden temperature changes, snow cover, vibrations in the ice sheet for the presence of people, repetition of loads and long-term stress. As safety threshold, it is advisable to have 18 cm thickness throughout the whole walking area, i.e. 1300 kg ice bearing capacity. We will see that Venetians risked walking on unsafe paths, sometimes with tragic consequences.

Threshold for ice-bearing capacity, i.e. load limit versus ice sheet thickness. The threshold is the black line; the safe area is on the right side, shaded, except for a band close to the threshold limit.

55The Venice authorities favoured safe walking paths with ice-bearing capacity to reach the mainland. Volunteers and workmen organized by the City were summoned to check the ice slab. Most often people walked in strict processional order, thinking of taking advantage of the involuntary check made by the preceding person. However, a long line of walking people is extremely dangerous because repeated loads over the same area, and within a short period of time cause, to ice fatigue and failure. The worst situation was with resonant vibrations caused, for instance, by the Dance of Moors, described below. Only in those cases that the thickness of the ice sheet exceeded in a high degree the threshold for ice-bearing capacity, it did not break down and could endure the above-mentioned heavy weight.

56The configuration of the Lagoon changed over time. From 1324 to 1683 the rivers entering the Lagoon were diverted to avoid the transport and deposit of mud and sand. From 1960 some canals were excavated to deeper depths for tankers and cruise ships. In the 18th century a massive dam was built to separate and protect the Lagoon from the Sea. All of these works changed a bit the response of the Lagoon. Today the central part (Northern Lagoon) is more protected against ice, while the Eastern part is more easily covered with ice, as we have seen in winter 2012.

57The list of the very severe (VS) and great winters (GW) from written sources analysed for Venice and Northern Italy is here reported. The bold date in the heading is the date recognized for the harsh winter. As common in climatology, the winters are indicated after the number of the year in Gregorian style, i.e. A.D. Winters with date followed by a question mark ? are not adequately supported and in general should be rejected, as specified. Notes or text reported in square brackets [ ] are our specifications added to make the comprehension easier.

58The historian Paul Warnefried known as Paulus Diaconus (720-799) who lived in Aquileia (100 km North East of Venice) wrote:“Blessed Pope Gregory died in the eighth Indiction of the second year of Emperor Phoca. He was replaced by Pope Sabinianus. In that year the winter was so harsh that it killed vineyards almost everywhere”.55 Sabinianus was elected pope the 13 September 604, indeed in the second year of reign (602-610) of the Eastern Roman Emperor Phocas.

58Year after Creation (YAF), also called Anno Mundi (AM), Latin for "the year of the world".

59Fritsche, 1555.

60Pilon,i 1607.

61Di Manzano, 1858; Other quotations in Hennig, 1904; Easton, 1928.

60Paulus Diaconus (who was contemporary) or Landulphus Sagax (who updated Paulus at the end of the 10th century) reported: “In the 23rd year of Emperor Constantine [i.e. Constantine V nicknamed Copronimus, ruled 741-775, i.e. the year 763] ... The same year, starting from October, a harsh and bitter cold was not only in our land, but even to East and much more to North. Because of the severe cold, the sea water became hard as a stone for over hundred miles and with a thickness of 30 cubits [1 cubit = 44.4 cm and 30 cubits = 13.32 m. This thickness is not realistic]... 57 After a long and detailed description of the situation in the East countries and the Bosphorus, the text reports that in February the cold continued with an exceptionally abundant snow and floating ice slabs, like icebergs “We ourselves were an eyewitness and with thirty companions went out onto one of them and played on it. The icebergs had many dead animals, both wild and domestic on them.” Exactly the same text is found in the Chronicle by Theophanes the Confessor. The many and detailed references to the area of Byzantine influence suggest that this text was written by Theophanes and copied by Paulus and/or Landulphus, including the personal detail of having been witness and having plaid on floating icebergs. The report was summarized by late authors who omitted the less credible details: "Year 4,727 after Creation58 - Year 764 A.D. At the beginning of October the cold became so extreme, that the Black Sea was frozen over for one hundred miles".59 “From October to February the winter was so cold that the sea froze over hundred miles and over thirty miles, the ice thickness was one cubit [1 Rome cubit = 44.43 cm] and it was hard as stone. People walked on it as they were on solid earth. Snow was so abundant that it formed mountains and exceeded 20 cubits [about 9 m]”.60 “In January and February the winter was so harsh, both in the Western and the Eastern [European] countries, so that all the rivers froze and in Constantinople, it was possible to go with carts over the sea”.61 Briefly, the cold was in the interval from October 763 to February 764; in October the seawater temperature is too high to freeze, and the most likely period is January-February, and February is suggested by the reference to the floating ice slabs.

61This event has been variously dated: 852, 853, 859, 860 and 864. The earliest existing Venetian history, the chronicle of Johannes Diaconus of the 10th century, said: “852 AD: Maurus [Businiaco or Busnago son of Geniano] was elected bishop of Olivolo [one of the islands that formed the actual City of Venice, named in 1091 Castello] ... In that year such a horrible freezing is mentioned at Venice, as never happened before nor will ever happen again"62. This citation has been reported dated 852 by Moisè Giuseppe Levi, Francesco Saverio Zanon and Arnaldo Segarizzi after Gallicciolli,63 who said: "An enormous extension of ice occurred at Venice when Maurus was elected bishop of Olivolo". According to Correr et al., Cessi and Cappelli 64 Maurus was elected in the Gregorian year 853. In the Civic Museum of Padua a copy of the will of the preceding bishop, Orso Partecipazio, is dated 853, so that the election of Maurus occurred in January or February of the Gregorian year 853 that is 852 More Veneto. Moisè Giuseppe Levi, Francesco Saverio Zanon and Arnaldo Segarizzi dated incorrectly this event 852 after Giovanni Battista Gallicciolli who never specified More Veneto because he considered it obvious.

65Monticolo, 1890.

66Einhard, 837.

67Rudolfus, 863.

68Relying on Rudolfus, the winter of 860 is reported among the severe winters in Europe by Arago, 185 (...)

69Toaldo, 1781; and Muratori, 1819.

62Giovanni Monticolo in his critical edition of the 'Chronicon' by Johannes Diaconus65 confused this event with another, which occurred in 860. He claims to quote the early Medieval German historians, Einhard (770-840), who wrote the first part of the ‘Annales Fuldenses: sive annals regini francorum orientalis’66, and actually confused him with presbyter Fuldenses Rudolfus who wrote the second part of the Annales in the 9th century and was contemporary to the event. Dating the event to 860, Rudolfus wrote: "The winter was exceptionally severe and long; it caused much damage to farming and trees. The snow was blood coloured. The Ionian Sea [a wrong term for the Venice Lagoon and the Adriatic] was severely frozen because of the glacial cold. For the first time traders arrived at Venice riding with merchandise, instead of sailing.67 The mention of the reddish snow preceding the freezing probably indicates a situation characterized by a northern flow of polar air encountering the southern warm and humid Sirocco, which carries reddish dust from Sahara. Since both the German Rudolfus in the late 9th century and the Venetian Johannes Diaconus in the 10th century affirm that the event was so severe as had never occurred neither before nor did it happen afterwards, only one of them seems to be correct. Undoubtedly the Venetian Johannes Diaconus is more reliable than the German Rudolfus, who was not very familiar with the geography and events in Italy. Probably Rudolfus associated the very severe winter in 860 Europe with news of an exceptional frost that occurred in Venice.68 Giuseppe Toaldo and Ludovico Antonio Muratori69, who were often used as authoritative sources, also followed Rudolfus. Toaldo wrote: "Years 859 and 860 AD. The Lagoon was frozen and wagons reached Venice". Some doubt arises whether: (i) the original source referred to two different winters, because the year 859 was missing in the Toaldo’s list of cold winters appeared in the 2nd edition; (ii) whether the source referred to 860; in such a case the source was not Venetian because it had used the More Veneto; (iii) Toaldo found two descriptions differently dating the same event.

70Fritsche 1555.

71Toaldo, 1770, 1781, 1797.

72Easton, 1928.

73Hennig, 1904.

63Markus Fritsche70 in his Catalogue wrote: "Year 4,826 after Creation - 864 A.D. Winter was long and vehement, much more than usual. Blood snow. The Gulf of the Adriatic Sea, where Venice was founded, was frozen over. Merchants transported up and down from the hinterland their supplies, with carriages and horses on the frozen marshes." Toaldo, who relied on Fritsche said: "In 864 the Venice Lagoon froze again.”71 Easton72 reported the winters 860 and 864, as they were two independent harsh winters, and for 864 relied on Fritsche and Toaldo. Hennig73 quoted 860 and 864 as harsh winters in England and Low Countries, citing some local sources.

64To sum up, it is uncertain whether the date of the cold winter in Venice was 853 or 860, or if that of 853 was very severe in Venice and 860 very severe in Western Europe. However, we should note that the expression "as had never occurred neither before nor after" in the chronicles is often found as a hyperbole and should not be taken literally. Very probably, the harsh winter was only one, occurred from 853 to 864. In this context the year 853 has the advantage of an early source with direct reference to Venice.

65Available documents are late. Umberto Locati reported: "In 1118 the cold was extremely severe, and for this reason the yield of the next year was extremely poor, and caused famine over the whole of Italy"74. The Cronaca by Girolamo Savina (ca 1588) for the year 1118 reports: "The Lagoon was so hard frozen as to bear the weight of people riding on horses. The frost killed vines and trees. Afterwards famine and mortality prevailed" 75. Gallicciolli76 quoted Savina: “A terrible frost. People rode over the frozen marshes. Famine and mortality happened the next summer” and dated the event 1118 and then in 1122 quoting “various writers, ancient chronicle” with identical details but different date. The harsh winter is also reported in the Cronaca by Friano degli Ubaldini77 (early 16th century), dealing with the same geographic area (Bologna), but dating the harsh winter 1119. These uncertain sources are generating a duplication of events. Francesco Saverio Zanon quoted some unspecified Annales Breves (the event is missing in the Annales Venetici breves 78), and dated the event within the time span 1118-1122.79 The most convincing date is 1119 that fits with the dating styles respectively used in Venice i.e. 1118 More Veneto (Savina) and in Bologna, i.e. 1119 More Romano (Friano degli Ubaldini).

66Four local chronicles: Annales Sanctae Trinitatis (12th-13th century) Filippo Garbello, ca 1232; Giovanni Codagnello, 1235, Carlo Sigonius, 1575, and Friano degli Ubaldini, early 16th century, who all relied on an unspecified source, reported that, when the Emperor Henry [V] died [i.e. 1126], Frederick and his father Conrad with the army of Henry [V] invaded Italy [...], The Po River froze, and supported the load of the invading army of the, with horses and carriages, and the whole region suffered a terrible cold.80 Another Emperor with name Henry (VII) has been found that invaded Italy in another occasion, i.e. 1306, and he too found the Po River frozen. This generated some confusion and might be suspect; however it is well documented before the next invasion in 1306. Toaldo duplicated this event in his publications in 1770, 1781, 1797 but dated it to 1133.81

67In the history of the Emperor Frederick, the German chroniclers Burchard and Konrad of Lichtenau (13th century) wrote: “A.D. 1157. Very abundant snow and unusual cold in the period of our Lord Passion. Great and extreme dryness summer for the whole summer”82In his list of extraordinary events Markus Fritsche summarized (without quoting the source): “Year 5119 after Creation, 1157 A.D. Very abundant snow and unusual cold; famine and dry summer followed it”83 After Fritsche, the event was reported by later authors. We note that in 1157 Easter fell in March 31st: snow and cold were the last week of March, i.e. too late to form ice on the Lagoon or the main rivers.

68Several chronicles of the Po Valley reported that the Po River was frozen for two months and the wine froze in the caves.84 The dates are: 1211, 1214 and 1216, two of them (1211 and 1216 by Sigonius). No specific documentation was found for Venice. As Codagnello wrote in 1235 and is credible, we accept the Codagnello's dating and reject the other dates (misprinted or duplicated).

70A number of chronicles mention a harsh winter with rivers frozen over from 1303 to 1306, as follows. Friday, January 11th 1303: some people told me that the Arno River was frozen over and people crossed it walking 88; 1304: the Po River froze, and carried the army of the Emperor Henry [VII]89 1305: the end of the winter was very harsh90; February 1305: very abundant snow91; 1306: Extreme cold for thirteen days in Parma and the Lombardy. All the rivers including the Po River were frozen over and in several parts it was possible to cross them on foot; boats could hardly move 92 ; rivers were frozen over and both foot and horse passengers and wagons too travelled over the ice.93 The winter was extremely severe and almost all rivers in Italy were frozen over, including the Adige River in Verona. It was possible to cross it on foot, on horses, or with wagons; many trees were killed. 94 In conclusion, the winters 1303, 1304 and 1306 fit the characteristics of GW. The date 1303 is supported by a contemporary author, although not eyewitness, with internal matching of day of the week (Friday) and date (January 11th 1303). It is not specified where the Arno River was frozen (e.g. in the mountain area?), and this fact is not confirmed by any other Florentine sources. Probably 1303 was a severe or very severe winter. Winter 1304 was cited by Giovanni De Cornazzano who related the events to the passage of the army of the Emperor. He made some confusion because Henry VII had invaded Italy in 1310 so that the winter should be moved to 1311. However, 1311 is not confirmed by other sources and should be rejected. Winter 1306 should be classified GW relying on a contemporary chronicle and two late compilations.

96Corio, 1474; a similar record in Lancellotti, 1627 and Toschi, 1876.

97Fritsche, 1555.

71A contemporary chronicle in Northern Italy reports: “Increasing cold from January to February. The Po River, the wine in barrels, wells and springs were frozen. Many trees were killed. Thursday February 20th strong and very cold wind; people could not walk on streets and who was there was killed. Snow and ice lasted till March, and even more in the shade. Wood became very expensive and was permitted to hunt pigs and other animals to survive. Streets were covered with half an arm [i.e. 34 cm; 1 Venice arm = 68.3 cm] thick ice slab.”95 “The cold was extremely intense. The Po River was frozen over for several days. Bread was hard and it was impossible to eat it without melting it on the fire.” 96 “Year 5280 after Creation; A.D. 1318. Extreme frost, winter very harsh.”97 No specific documents regarding Venice have been found for further details.

72We have late quotations, not specific for Italy. Marcus Fritsche wrote: “Year 5303 after Creation; A.D. 1341. The cold was so intense in this winter, that people in Livonia [Baltic region] had lost nose, fingers and so on for the cold”.98Toaldo, without quoting the source: “1341. Very harsh winter.”99 We haven’t found further support to confirm this event in Italy.

73The harsh winter with snow, long lasting ice and all rivers frozen over (in particular the Arno River) in the Florence region is mentioned by the witness Matteo Villani100 who dated 1354 but used the Incarnation calendar, Florentine Style. No documents have been found about Venice.

75Clemente Miari, who wrote his chronicle between 1383 and 1412 and probably was an eyewitness said: “On January 22nd it was possible to reach Venice from San Giuliano [in the Venice hinterland], walking and riding on the frozen Lagoon. We did it with eleven horses".102

76“1407. Winter extremely cold; the year was nicknamed the year of ice”.103 “Harsh winter, with frozen rivers and lakes” according to late 18th and 19th centuries historians, who did not specify their source.104 The event is not adequately supported by contemporary documents.

78“The winter was exceptionally harsh. All rivers were frozen, and it was possible to cross them on foot or with pack animals and even with wagons. Vineyards were destroyed and next year there was scarcity of wine. It was possible to cross the sea and reach Venice”.106 The event is quoted by a late source and is not supported by other sources. Maybe a duplication of 1413, but with some additional emphasis. This winter should be rejected.

79"Beginning on January 6, 1431, the frost was so terrible at Venice, and the ice was so extensive, thick and hard, so that it was possible to go from Venice to Mestre over the ice sheet. A cart drawn by a horse arrived at Venice from Mestre to carry a bride from Venice to Mestre. The ice lasted till February 22nd."107 Erizzo wrote More Veneto and, consequently, Levi, Zanon and Segarizzi108 incorrectly dated to 1431 without considering the time difference.

80A series of chronicles span from 1441 and 1443, explicitly mentioning December. This makes particularly difficult to distinguish between the two years and the risk of duplications. A cold 1442 winter (no month specification) with abundant snow and the Po river frozen and supporting people and carriages is mentioned by Cherubino Ghirardacci (1568), Guglielmo Schiavina (ca 1617), Cristofaro Orefice Saraceni (1619), Compendio istorico del dominio e governo della città di Ravenna 17th century and the Cronaca di Ravenna (end 18th century). Abundant snow and extreme cold starting from December 24th 1442 and lasting for three months is mentioned by Marco Antonio Bianchini 1513109. The contemporary Cattanio de’ Cattani specifies: “[1442/43]: This was the second year of ice. The Po River in Ferrara was frozen over, supporting carriages with horses … In Venice the Grand Canal was also frozen, and people and animals could go from Marghera to Venice [crossing the frozen Lagoon]. Several vineyards and trees were killed …” 110 Two contemporary Anonymous sources, i.e. Cronica di Bologna and Diario Ferrarese,111 conveyed a similar report. One hundred years after the event, the Venetian historian Marino Sanuto without quoting his sources wrote: "The Lagoon froze in December [1442] and the ice held the weight of people walking from Mestre to Burano Island. The same occurred in 1475, 1476 and 1490. It snowed continuously for 12 days."112 Other chronicles from the 16th to the 18th also reported on this winter, however, without indicating their sources.113 The conclusion is that two consecutive harsh winters occurred: the winter 1441/42 could be classified severe to very severe, and the 1442/43 was a great winter. The accurate history book by Cardinal Cesare Baronio reported: “Year A.D. 1441, [Pope] Eugenius IV [year:] 12, Friederick III [year:] 3, Johannis VII [year:] 24. At the end of the year, from December 7th to February 7th the cold in Lombardy [region some 200 km West of Venice] was so extreme that the Po River was frozen over and supported horses and carriages. In the region of Ferrara [some 100 km South West of Venice] people organized a banquet on ice and this feast was crowded. The snow was so abundant as never occurred in living memory”114

81According to Bernardino Zambotti, who wrote 34 years after this winter, extreme cold was from October 1476 to March 1477. In 1477 the Po River froze and it was impossible to grind wheat.115 However, no further support has been found. Probably the winter was severe with a local problem of ice in shallow channels used to bring water to mills, or this is a duplicate event; see 1487?, 1491.

82"An exceptionally heavy snowfall occurred on Christmas night [December 25th 1486] and it continued snowing for a month. On the mainland all the vines died. People rode from Marghera to Venice over the thick ice. The mayor of Mestre arrived in a coach as far as the island of San Secondo. (...) Wherever man looked around Venice, snow could be seen. The canal between Piazza San Marco (the heart of Venice) and Giudecca [an island directly in front of it] froze, and the people could cross on foot the canal without risk. Boats were drawn from one bank to the other with a hawser." The text, very similar to the description made by Cardinal Pietro Bembo for 1491, was reported by Secondo Lancellotti, but dated 1492116, and Gallicciolli, relying on obscure Ancient Chronicles'117; finally in the 20th century Zanon, who relies on an undated chronicle, Cronica Marciana, kept in the Marciana Library at Venice.118 However, the severity of the winter is not confirmed by other independent sources outside Venice and is very probable an error by Gallicciolli or his documents. We are forced to reject this event that very probably is a duplicate of 1491.

83This winter is documented by tens of sources outside Venice and some specific of Venice, here reported. A chronicle contemporary to the event, the Cronica de Venexia, reports: “In 1490 [More Veneto] on January 10th Venice was frozen so much for the extreme cold that people and animals with food could cross the Lagoon from Venice to Marghera, i.e for three miles of ice above the marshes” 119. The Venetian humanist and historian cardinal Piero Bembo, who was eyewitness when he was 21 year old, wrote: "Winter 1490 [MoreVeneto], was terrible, cold and long, especially because of the snowfall. All the Lagoons around Venice were frozen. People came from the mainland safely on foot and on horsebacks bringing provisions to Venice. The mayor of Mestre arrived in coach to San Secondo Island, located in the middle of the Lagoon. Some riders jousted with lances on the Grand Canal, where only large ships usually go. The water was frozen because of the terrible cold and snow".120 The text of Bembo was famous and summarized by late chronicles: Codice Gradenigo (18th century) and Gallicciolli 121; in addition it was misleadingly quoted by Toaldo who dated to 1492 122 and Zanon to 1490 123 creating duplications. Other sources deal about this extreme cold in Italy, with the main rivers frozen over and supporting people and carriages, wine frozen, trees killed.124 Some of them report about Venice, and Jacopo Rizzoni in particular mentions that some wolfs arrived in Venice crossing the ice 125.

84This winter is found in late collections, e.g. Lancellotti who was used as a secondary source. “In the time of Pope Julius II, who was sitting in 1503, the winter was extremely cold, and the Po River was frozen over. The ice was so thick that the artillery with guns of the Pope could cross it”126 Lancellotti relied on an obscure quotation "P. Iou. Lib.2 vit". In reality, Lancellotti wrote that this winter happened in the time of reign of Pope Julius II della Rovere, i.e. 1503-1513, and 1503 is only the date of its election. The problem is that in the side gloss heading Lancellotti wrote 1503 as reference. Therefore the date 1503 is misleading and the information should be referred to 1511.

85A number of chronicles of the 16th century, such as: Niccolò Seccadenari and the famous historian Francesco Guicciardini127 mention severe cold, and the most relevant was that in January the Po River froze (not specified where), and that it carried the weight of Pope Julius' II army that was engaged in the siege of Mirandola, 158 km South-West of Venice. Very probably, the winter was severe to very severe; we, however, suppose that in Venice it did not reach the GW severity level, for the lack of local records confirming ice.

86Jacopo Rizzoni128, an eyewitness living in Verona, some 120 km West of Venice, reports that the Adige river was frozen over near a bridge, and people crossed it on foot. No chronicles mentioning ice on the Po River. The contemporary Sebasiano Mulione129, living in Gemona some 130 km North-East of Venice, mentioned three windy and extremely cold days in February 1514. The contemporary sources in Venice do not mention anything that may be related to a particularly harsh winter. The most probable classification is “severe”. The winter was described with GW characteristics in late and not adequately justified sources. Quoting the Manuscript Svajer No. 865 (end 17th century), Gallicciolli and Zanon 130 reported: "The Lagoon was frozen from Fusina, [on the mainland, North-West of Venice], to San Giorgio Island [in front of Venice]”. Arago mentions that the winter was very severe in the Flanders, with carriages crossing the iced water bodies131. Gallicciolli quoted 1514, and its general use is More Veneto, so that the winter should be 1515. Easton in the 20th century relies on 11 sources about this winter in Europe but with date spread from 1513 to 1515. In particular, he quotes “1515: Thames frozen and used as a highway. Carriages passed over on the ice from Lambeth to Westminster (W. Thornbury)” without further details about Thornbury and the dating style.132 The same quotation is in Lamb133. The event is not adequately supported, at least for Venice.

87The winter was described by the contemporary Tommaseo De’ Bianchi nicknamed Lancellotti, living in Modena, 150 km South West of Venice. “Extreme cold started the day of St Sebastian [20 January] with ice, strong wind and dry snow. Thursday 22 some people arrived from Venice told me that the ice covered the Lagoon for three days and it was possible go from Venice to Marghera [on the hinterland] on foot. Boats were kept outside”134. The Venetian Girolamo Savina in 1558 gives an account of the situation: “in January 1548 [More Veneto] the cold was extreme, with a lot of ice. The canals were frozen over and it was possible to go from the Giudecca [island] to [St] Baseggio [on the Southern Venice border, i.e. it was possible to cross the Giudecca Canal] walking on ice. It was possible to reach the hinterland because all canals were frozen. Six persons inside a ship trapped in the ice were dying for the frost. Two Greek men reached them and brought them back, but this was useless. They [i.e. the Greek men] were rewarded with two ducats135 each one.” 136 This fact was also reported by Cesare Clementini in 1617 who quoted Valerio Monticoli, a chronicler in Ravenna137 . The famous architect Vincenzo Scamozzi who was working in Venice in that time was eyewitness and confirmed the extreme cold and impressive ice138, dating 1548 [More Veneto] i.e. 1549 [More Romano].

139Della Corte, 1744.

140Gallicciolli, 1795.

141Levi, 1845.

142Zanon, 1933. The eyewitness Cristofolo Zaccaria was an officer of the Offizio della Giustizia Vecch (...)

88Late chronicles too reported the event. Della Corte 139 reported about vineyards, olive and other trees killed in the hinterland. Gallicciolli quoted the Manuscript Svajer 865: “1549. The Lagoon froze, including the Giudecca canal as far as Murano” 140. The manuscript was evidently written More Romano because the date is 1549. This is misleading because Gallicciolli normally uses the More Veneto and who reads Gallicciolli is induced to move to 1450. Levi141 relied on the Manuscript Svajer 865 and the text is identical to Gallicciolli. Zanon quoted an unknown source: “The frost began on January 21st, 1548 [More Veneto]; the canals crossing was made with boats drawn to and fro with hawsers over ice. People went on foot from the Zattere [Southern side of Venice] to the Giudecca [island facing the Zattere] (Cristoforo Zaccaria)”.142 Then he continued reporting and quoting the above text by Savina. After he reported as a distinct event for the next year: “1549. The Lagoon froze, including the Giudecca canal as far as Murano (Ms Svajer No 865)” making a duplicate for the More Romano used in the source.

89Umberto Locati, living in Piacenza, mentions that the Po froze over and dated the event to 1559 [Incarnation Style used in Piacenza, i.e. 1560 A.D.].143 A late 17th chronicle mentions a harsh winter in 1560, without indicating the source.144 Quoting the 15th century Manuscript Svajer 421145, now lost, Gallicciolli wrote: "1560 January. Snowfall continued for 3 days and the canals were frozen over. (Ms Svajer 421)”146 Very likely, the Ms Svajer 421 is based on the More Romano.

90The contemporary Codex Cicogna147 reports: “A terrific cold happened this year, that exceeded the limits of the nature and the climate. The Doge Mocenigo died after having ruled for eight years and six months…” The Doge Alvise Mocenigo ruled from 1570 to 1577. The Codex Cicogna 262 was misdated 1567, and we should assume 1577.

91The famous architect Vincenzo Scamozzi, active in Venice, mentions that he was eyewitness of the Lagoon the frozen over in 1581, 1594 and in 1607, when the northern winds brought an exceptionally severe frost to Italy and part of Europe, and it was possible to cross on foot the ice sheet formed on the Lagoon and the canals and to safely reach the Giudecca, Murano and other islands. In addition, he specified that in the above events the low rate tidal exchange was crucial for the formation of the ice sheet.148

92Vincenzo Scamozzi claims of having been eyewitness of this event as well (see winter 1581). The frost was reported by the contemporary Cesare Campana (living in L’Aquila, Central Italy), who was the source for Secondo Lancellotti. In turn, Lancellotti was the major source for Toaldo 149. Campana wrote: “1594 exceedingly low cold in Italy. The winter was dry, long and extremely cold. Not only rivers, but the Venice Lagoons too were frozen over for several days, and citron orange and other fruit trees, although located in mild regions became useless”150. Lancellotti quoted: "In Flanders, the Rhine, the Scheldt and other Rivers were frozen over; in particular, in Italy the Venice Lagoons were frozen. (Caes. Camp. 15)." 151 The same text was reported by Tilloch152. According to Arago and Hennig153 (who relied on Lancellotti , Toaldo and probably Tilloch), the Rhine and the Po Rivers froze. The sea was frozen over in Marseille and in Venice.154 Easton155 dates this event to 1595. However, since the late authors rely on a number of uncontrolled documents they provide inaccurate dating.

158Sansovino, 1581; Sansovino and Stringa, 1604. Sansovino was died in 1586, i.e. 5 years after his bo (...)

159Scamozzi, 1615.

93The dating is according to 18th and 20th centuries sources that cite the Manuscript Svajer No 865 that reports on the public prosecutor's, Francesco Zorzi, who died due to the intense cold while crossing the ice sheet from Torcello Island to Venice.156 According to Serafino Pasolini and Benedetto Fiandrini “The horrid cold of this winter killed in Ravenna (100 Km. South of Venice) many people, animals, vineyards and trees”157. Both authors, however, do not indicate the sources they used. In addition, this winter is not recorded by two key persons living at that time that should have mentioned it. The first was Giovanni Stringa who updated from 1581 to 1604 the Francesco Sansovino's book adding a number of climate-related events 158. The second key person who missed this event was Vincenzo Scamozzi.159 One might suppose that Scamozzi missed this frost because from 1596 to 1601 he was working outside Venice, at Padua and Vicenza. However, these two cities are close to Venice, with the same climate and it is very unlikely that passed unobserved. Briefly, this frost is not supported by two key local contemporary sources interested to climate. We should conclude that 1598 is a duplicate, possibly a misprint for the well documented 1594.

94"Beginning on February 2, 1602 [More Veneto], the Lagoon and all the canals in Venice froze over for 8 to 10 days." This event was added by Giovanni Stringa in the 2nd posthumous edition of the Sansovino's book, compiled in 1604.160 The date was misprinted 1601 by Gallicciolli, and the error was transmitted to Levi, Zanon and Segarizzi. 161

95Scamozzi, who may have been an eyewitness, mentions that in February 1607 the Lagoon and all the canals were frozen by an exceptionally cold wind from North combined with a modest tidal range, and that it was possible to reach on foot the Giudecca, Murano and other islands162. Giustiniano Martinioni that updated in 1663 the 3rd edition of Sansovino's book wrote: "After the beginning of this year (i.e. March 1608), the winter was unusually severe. Due to an exceptional snowfall, it was impossible to walk in the streets or go out through the door".163 In the late 18th century Toaldo reported the severity of the winter and the exceptional snowfall.164

96Tilloch,165 later copied by Millner166, and followed by Arago and Easton, reported: "In 1621 and 1622 all the rivers of Europe were frozen, and even the Zuidersee [the Netherlands]. A sheet of ice covered the Hellespont; and Venetian fleet was chocked up in the Lagoons of the Adriatic." Arago167 wrote the same, almost with the same words, except for the winter 1720-21, and adding the Baltic Sea and the Provence, and disregarding the Hellespont. He specified that he relied on Sethus Calvisius.168 Hovewer, the book by Calvisius was published some 20 years before the event that is obviously missing. Consulting the next posthumous editions of this book, we found the third edition updated by J. Zhym and published in 1629, almost contemporary to the event, that reports: “1621 AD. The cold was very intense for the whole month, and a part of the Baltic Sea was covered with a thick ice sheet”.169

170Spaccini, ca 1636.

171Toaldo, 1770, 1781, 1797.

97However, Venice and the Adriatic Sea are not mentioned. Furthermore, although this was a well-documented period, no confirmation has been so far found, except for some snow, cold and ice in Modena in 1621. 170 Giuseppe Toaldo, in his list of the cold winters includes 1624 and 1625, but without notes or comments, or specifying where in Europe or Italy as he did when he found some precise information171. The dates 1621, 1624 and 1625 should be considered misleading, misprint or duplication of other events and should be rejected.

172chains were drawn across the river to avoid the passage of non authorized boats.

173 Biancolini, 1749.

174 Easton, 1928; Hennig, 1904.

98Only Giambatista Biancolini, a chronicler who one century after this winter updated the chronicle of Verona by Pier Zagata, mentioned an intense cold: “For the intense cold the Adige River was iced from the chain172 of Victory [a gate in the city walls] to the chain of St Zeno [another gate]”.173 Easton and Hennig174 did not mention this winter at all. In the contemporary chronicles in Northern Italy no mention has been found that may justify a severe winter in Venice and the winter should be rejected from the list.

99This was a renamed harsh winter in Marseille, on the southern coast of France. The astronomer and philosopher Pierre Gassendi working at the University of Aix-en-Provence was a witness and ten years later recorded [in Latin] the weather and astronomic observations in his daily log. The most interesting comments are: “Day 30 [December 1637]. Clear sky in the morning; the cold was very intense. At 6 p.m. some snow, then again. … Day 31. In the morning sky mostly clear, but cold extremely intense, snow very cold and then becoming compact like ice. … Year 1638, month January, Day 1. Sky mostly clear and always very intense cold. … Day 2. Clear sky in the morning and always very intense cold. … At noon cloud cover, with tendency to melt, but snow in the evening. Day 3. Snow again but rain too, and for this reason much of the snow was melted. Day 4. Weather lost it chill and almost all the snow was melted. … Day 15. All day rain. Day 16. Chorus Wind [from North West] very cold. Day 17. Cold very intense, but no wind. Day 18. Some cold, but sunny day till sunset. Day 19. Cold a bit attenuated. Day 20. Cold was worsened and the wind blew stronger, and prevented from the traditional procession of St Sebastian. Days 21 & 22. The air was cold enough. Day 23 Cold very intense and Chorus Wind very strong. Day 24, evening. … Wind blew very strong and entering everywhere; the cold was beyond living memory. … Day 25. Always strong wind and very intense cold. Day 26. The same. These days should be remembered for people lemon, fig and olive trees killed by cold. The [water] in the port of Marseille formed ice around vessels, etc. Day 27. Less intense wind and cold. Day 28. Wind and cold over.” 175

176 Papon, 1786.

177 Arago, 1858; Mathieu, 1879; Villard, 1887.

178Easton, 1928.

179Hennig, 1904.

100One and half century later, the same winter is found described at increased severity level: Abbot Jean Pierre Papon, member of the Academy of Marseille, in his history of Provence, wrote without quoting the source, very likely Gassendi: “1638. The Count of Alais arrived the first days of January… In that period the winter was very severe and the water of the port of Marseille froze around the galleys”.176 The text by Papon was copied by several chroniclers and historians, including Arago, Joseph Mathieu and Marius Villard177 and became famous, while Gassendi remained almost unknown. Surprisingly, Easton178 wrote that this winter had no comments except for Papon (he missed Gassendi) and Hennig179 had no sources for this winter; as a consequence, he considered it normal.

101In Marseille the cold was intense and even extremely severe for some days, i.e. from December 31st to January 2nd and then from January 16th to 26th. The first period, i.e. three days, was too short to cause severe consequences, but the second period of ten days was long enough and needs to be clearly interpreted. It is not clear whether the whole port was frozen over (that requires a long period of very intense cold), or only some ice was seen on the keel side above the waterline for frozen splashes (that is possible in a relatively short period of intense cold). In effects the text does not quote “the water in the harbour was frozen over and the galleys were chocked up”, but “the water froze around the galleys”, i.e. the galleys were covered of ice, not the sea. An example of the second interpretation is given by the gondolas with ice in February 1929 (Fig.5).

102The weather log by Gassendi suggests a flow of arctic or polar air crossing Europe and entering the Mediterranean close to Marseille, being channelled by the Pyrenean and the Massif Central mountains. The persistence of the circulation is generally due to a blocking high-pressure over Scandinavia. If the pressure pattern brings a violent flow of very cold air, the same situation is found in Northern Italy.

180Romani, 1829.

103In Italy, the late chronicler Giovanni Romani quoted a contemporary act of notary E. Lodi that in the winter 1636 the cold was severe with ice slabs on the Po River and several vineyards damaged or killed; in 1637-38 some vineyards were damaged or killed again180. In other words, the winter 1638 was not worse than 1636. We have consulted several contemporary documents in Northern Italy, with several detailed notes, but no mention has been found that may justify a very severe winter in Venice. The circulation caused severe problems in Southern France, but was not strong enough to enter Northern Italy and reach Venice. For this reason in Marseille the winter was a GW (if the seawater in the was frozen over) or a VS winter if only the keels were covered with ice; however, in Northern Italy this winter left no memory of it.

104In 1820, Alexander Tilloch wrote: “The winters of 1658, 1659 and 1660 were intensely cold. The rivers in Italy bore heavy carriages; and so much snow had not fallen in Rome for several centuries. It was in 1658 that Charles X of Sweden crossed the Little Belt over the ice from Holstein to Denmark with his whole army, foot and horse, followed by the train of baggage and artillery”181. Thomas Millner copiedthe same text.182 Arago183 reported the story of Charles X, the snow in Rome, and very severe cold and ice from December 24th 1657 to the end of February 1658, when the Seine River outflowed. However, no mention of frozen rivers has been found in Northern Italy sources and the fact should be rejected. The foreign sources refer to France and other northern regions far away from Venice that remained unreached by the polar air circulation.

105One hundred years later, in 1796, Benedetto Fiandrini wrote: “1684. This year the winter as so harsh that all wells were frozen over, … not only in Romagna, but everywhere in Italy” 184. Serafino Pasolini wrote substantially the same, but added that many animals and vineyards were killed by frost. 185

186 Gallicciolli, 1795.

187 Manley, 2011.

106"In January 1684 the Lagoon froze. It snowed continuously for 10 days. The frost killed all the vines and many people". This event was reported by Gallicciolli,186 who quoted: “Ancient Chronicles”. Surprisingly, he dated this and the next two events according to the More Romano probably used by the source instead of the More Veneto that he hitherto used. It should be noted that in the same year 1684, the Thames River froze in London. In other words, the frost extended over most of Europe.187

107This was one of the most severe winters of the last millennium, supported by hundreds of sources. We have selected the following five descriptions, made from eyewitness and others scientists who lived not long afterwards.

188Garzoni, 1716.

108The Venetian senator Pietro Garzoni, who was eyewitness, reported that Fredrik IV, king of Denmark, arrived in Venice at the end of the year 1708 [More Veneto that means January or February 1709]. A welcome programme was prepared with great festivities to be held in his honour, especially because the period was Carnival. However, not all the planned festivities were possible because of the extremely severe cold. "The cold severity exceeded the thresholds established by the nature and the climate. All the internal canals and the Lagoons became petrified by cold, and boats could not move. Boats transporting food and supplies for the survival of the City were moved with pickaxes used to the best of the power of the Arsenal workmen"188

189Cronica Gradenigo, 18th century.

109Cronica Gradenigo: “In 1708 [More Veneto], during the king's of Denmark stay in Venice when Alvise Mocenigo was the Doge, an extreme cold started in the Epiphany day [i.e. January 6th]. Many people were killed by the cold, and the Lagoons were frozen over with thick ice that carried people, horses and carriages from Mestre [in the hinterland] to Venice".189

190 Gradenigo, 1774.

110Gradenigo's Annales were similar but dated it to the "the night of January 5th, 1708 [More Veneto]"190.

191 Gallicciolli, 1795.

111“The 6th January 1708 [More Veneto] the horrible cold started. The Lagoons were frozen over for about 18 days. Food supply was made with carriages. Similarly in 1740, 1758 and 1788.”191

192 Riva, 1713.

112The contemporary Giuseppe Riva, living in Modena, reported: “January 26, 1709. We received news from Venice. They mention that the cold of this winter exceeds any other one could remember for the last 25 years. All canals are frozen over and there is a risk that all business and transport of supplies will stop”.192

193 Palladio degli Olivi, 1767.

113“The year 1709 was famous for the severe frost and the Venice Lagoons frozen over, holding people walking on ice. Heavy snowfall everywhere, which caused to severe famine. Frost and snow lasted till the end of February, and it was impossible to transport burning wood, crops or other supply with carriages. March was followed with epidemic and illness, and many people died”, according to late 18th century Palladio degli Olivi.” 193

194De Grisulphis, 1876.

114“The frost was so severe that both the Venice Lagoon and the Po River were frozen over. It was possible to safely cross the river with carriages, and artillery. The ice on the Lagoon was noxious to Venetian trades because transports were necessarily on ice, and were more difficult that using boats. Vineyards, olive, nuts, orange and lemon groves and other trees were killed.” 194

196Invented by Guillaume Amontons in 1702 is the first air thermometer, used in association with a bar (...)

197 Poleni, 1709; Camuffo, 2002a, 2002b.

198 Biancolini, 1749.

116Unfortunately, no temperatures of this winter were recorded, although Giovanni Poleni at that particular time used in Venice an Amontons' thermometer196 to measure this winter.197 Forty years later, Biancolini' Chronicle, written at Verona, 80 km West of Venice, reports that “the extreme cold began on 6th January and killed several trees and especially vineyards and olive trees. The thermometer invented by Mr. Réaumur of the Science Academy, Paris, dropped to fourteen degrees below zero”.198 The level -14 °R=-18°C. Nevertheless, Biancolini did not specify when and where the observation was made (e.g. Verona? Paris?), thus making uncertain his information.

117The Venetian eyewitness Antonio Benigna wrote a book of his memories, from 1714 to 1760, where we read: "17 January 1715 [More Veneto]: People reached Venice from Mestre crossing the ice, bringing animals and other supplies. This until 20 January.” Gallicciolli wrote: “In January the cold was not less severe than in 1709, but was shorter. The Lagoons were frozen over”.

119In his book of memories, Antonio Benigna wrote: "On January 1st, 2nd, and 3rd, 1754 [More Veneto] there was severe frost; on the 4th, 5th, 6th and 7th the frost was even more severe, fresh wind blew and ice developed on the Lagoons. On the morning of the 8th the wind dropped, and the Lagoon was fully frozen over. Afterwards the weather was milder. However, on the 9th two soldiers came from Mestre on foot and 6 persons went on foot from Venice to Mestre and returned the same way with muttons. On the 11th a public procession carrying the Virgin took place at St Marc Square, praying for rain. People went from Mestre over the ice, transporting food supply. On the 21st, 22nd, and 23rd fresh wind blew again. On the 24th the wind dropped and on the evening of the 25th, the Lagoon was once again covered with ice. The weather was fine but very cold, especially at the beginning of February. On the 4th and 5th the Lagoon was frozen over again and the canals in Venice too. On the 6th, light snow fell during the night. On the 7th, the ice melted and the Sirocco wind blew for the next days. On the 13th it rained. On the 18th, the ice disappeared.200

201Anonymous, 1755 “Letter Codice Gradenigo”.

120A long letter by an Anonymous eyewitness, dated February 5th, 1754 [More Veneto],201 described in detail the supply of food when the Lagoon was frozen. The ice appeared on January 6th and lasted for eight days; then it started to melt, disappeared and afterwards, returned again. The author says that he has measured the temperature with his thermometer and that the air temperature of the second period was the same as in the first period (6th-14th January), without specifying the degree.

202Anonymous, 18th century “Cronica Gradenigo”.

121Another contemporary said: “January 8th 1754 [More Veneto]. There was severe frost and the Lagoons, the internal and the external canals were frozen over. This caused shortage of burning wood and water. The sky was clear. Workmen were sent from the Arsenal to cut the ice slab”.202

203Temanza, 1755.

122A weather log with daily instrumental observations and notes, made in Venice by the scientist Tommaso Temanza, a former pupil of Giovanni Poleni, reads: "January 6th: extensive ice on the Lagoon. 13th: sky less clear and ice is melting. 24th: sun and clouds. Once again ice covering the Lagoon. February 6th: ice is melting". The observations included: Moon phase, air pressure, temperature, thermometer, tide, state of sky, wind and rain.203 However, the temperature is not easily understandable, because Temanza used an Amontons thermometer with unknown calibration, and the readings are expressed as derived from the average temperature in Venice. It might be possible to reconstruct the scale by comparing to the contemporary series in Padua; however, such a study would require a very long time, not fully justified since it would not add much to our knowledge.

204Camuffo and Jones, 2002; Camuffo and Bertolin, 2012.

123Unfortunately, a number of persons, including the above-mentioned Temanza, used their own personal thermometer scale that did not display the actual temperature at Venice. However, we know the temperature from the measurements taken in Padua by Giovanni Poleni and Giovan Battista Morgagni (see later).204 We should note that the temperature in Padua dropped to -7°C on January 10th and -6.5°C on February 5th; Padua is near to Venice and the temperature is similar, i.e. within ±2°C.

205Toaldo, 1797.

124Relying on Temanza, Toaldo wrote 45 years later: “Year 1755: In January the Lagoon was twice frozen over. The ice held the weight of people. Temanza measured the ice thickness and it was found to be 15 Venetian inches, i.e. 43 cm (1 Venice inch= 2.898 cm). No snow."205 An ice sheet 43 cm thick may bear up to 7500 kg.

125The velocity at which ice was formed on January 6th was impressive. All the canals were frozen over in a few hours. Initially the Lagoon was rough because of the strong wind. In the marsh areas, where water was shallow and colder, the ice slab kept the form of waves. We cannot know whether the water had formed so many freezing nuclei that determined an instantaneous transition, or the rough appearance was simply determined by wind driven water splashing on already formed ice and then building-up illusion of waves. The thickness of ice was two Venetian feet, i.e. about 70 cm (1 Venetian feet = 34,77 cm). It should be noted that this thickness is almost twice as much as the measurement taken by Temanza; however, this difference can be explained by the location and the time the measurements have been taken.

127One hundred years after the event, the climatologist Francesco Zantedeschi wrote: “December 10th, 1774 the Lagoon had ice that could hold people and large weights”207. According to the convention in use in climatology, this means winter 1775, the winter being characterized by the January date. However, no confirmation has been found in the local or other documents.

128The contemporary Codex Gradenigo XXI (Anonymous, second half of the 18th Century) reported that January and February were extremely cold, with snow and wind blowing from North, and persistent ice, both inside and outside. The cold was similar to the level reached in 1709. This caused lack of water, famine, illness and death in Venice. Newsarrived about the Rhone River supporting carriages, extreme cold in Ratisbon (Germany) and Madrid, with killed people and animals. The temperature record by Beccari in Bologna was interrupted on 18th January 1766 for the death of the observer, and reached -8°C (Beccari, 1766). In Padua, the monthly average of the observations taken by Giuseppe Toaldo was -4°C. However, no specific news was found about ice on the Lagoon. Possibly, the cold happened in periods of lunar conjunction when the tidal exchanges are maxima and bring in large amounts of mild marine water.

129Eye-witnessing this event, Giuseppe Toaldo wrote that in January the Lagoon around Venice and some canals were frozen over impeding access to the hinterland. The Republic sent some workmen to break the ice sheet for the passage of some boats.208

130Giuseppe Toaldo noted: “The past December 1784 was very harsh for the cold” 209. The contemporary Giuseppe Gennari, living in Padua, in his diary noted: “The mercury in the thermometer dropped by 8 degrees [°C] below zero. The Lagoon was frozen over and for two days we had no mail from Venice”.210 Zantedeschi added: “January 1784. The Lagoon was frozen over impeding access to the hinterland and keeping Venice without contacts. A number of boats were trapped in the suddenly formed ice”.211

131Reliable instrumental readings were taken by the Patriarcale Observatory in the centre of Venice that recorded -13 °C on January 12th. In Padua, Toaldo noted in his daily logs at the Specola Observatory that the Lagoon was frozen and the air temperature readings reached -15.4 °C in December 30th 1788 and -15.5 °C on January 1st, 1789.

212 Gennari, 1982-84.

213 Cavanis, ca. 1858.

214Zantedeschi, 1869.

215Levi, 1845, 1858.

132Giuseppe Gennari in his diary the January 4th 1789 recorded that the Lagoon was frozen in the shallow part of the marshes and that he got the announcement that the Po River too was frozen.212 The event was carefully described with many colourful notations about the daily problems and social implications in mid-19th century in the Anton Angelo Cavanis' Diaries213. A few details, like the frozen wine, are similar to Virgil in Georgics, book 3, lines 360-366: “Sudden ice crusts form on the running stream, and the water bears on its surface iron-bound wheels – once welcoming ships, but now to broad wagons! Everywhere brass splits, clothes freeze on the back, and they cleave with axes the liquid wine; whole lakes turn into a solid mass, and the rough icicle hardens on the unkempt beard.” We will only quote and summarize a few climatologic notes. From Cavanis' Diaries: "Because of the extreme cold which began in the second half of the month with heavy snowfall, the Lagoon froze on December 28. On January 30 people began to cross on foot the Lagoon from Venice to Mestre and vice versa". This situation lasted for many days so that Venice was hit by famine. "All the Lagoons and the internal canals were frozen over, except for the Giudecca canal which was only partially frozen because there the tidal currents are stronger. Similarly the canal to Fusina was filled by slabs of ice from other parts of the Lagoon, but people could cross it on foot safely". Ice started to melt on January 10th, 1789. Zantedeschi214 reported: “ice in December 1788 and January 1789 when the Lagoon was crossed on foot for eighteen days, until January 14th. The thickness of the ice slab reached 8 inches [i.e. 23.2 cm; 1 Venice inch = 2.898 cm]”. The winter was also commented by Levi, who contacted several eyewitnesses and reports that the temperature dropped 18 degrees below zero. 215 Probably he intended -18° Réaumur scale because -18°R =-14.4°C, more similar to the official readings.

134On January 8th a violent Bora wind blew polar air and it was followed by snow from 9th to 11th and then, in the 13th. The temperature dropped to -6°C and the Lagoon started to freeze. The 17th the temperature returned milder and with sunshine, melting the ice217. The event, that falls within the definition of one week VS winter, was well known and was quoted by leading authorities, such as François Arago and Easton.218

135January was started very cold, with ice, hoarfrost and clear sky. The coldest day was on 4th, when the thermometer reached -6 °R (-7.5°C) and the Lagoon was frozen. In the following days, snow and cold that lasted until the 17th when the Sirocco wind brought rain.219

136January. The Lagoon was frozen over and sustained the weight of people in the area between the Fondamenta Nuove and San Michael Island. This event was engraved on a pillar of a portico, called "Sotoportego del Tragheto” (i.e. portico of the canal crossing), near the Basilica San Canzian, Venice: “[For] eternal memory of the year 1864 and the ice in Venice, when people walked in procession from Fondamenta Nuove to San Cristoforo”. Bortoloni composed in that year a popular song to celebrate the winter220. The instrumental records taken in the Patriarcale Observatory, Venice, and in Padua221 that we have recovered and analysed show that the temperature was low, reaching -11.6°C. However, the severe cold was too short to form a thick sheet over the whole northern part of the Lagoon and to support the weight of people. The winter severity should be classified VS.

137Starting in November and then for most of December 1879 polar air from Russia blew over Eastern Central and Western, Europe, with abundant snow and extremely low temperature, especially in France where the Seine River was frozen over. 222 Although this was a GW for most of Europe and was harsh in Northern Italy too, documented by the regular thermometric records, no mention has been found about ice on the Venice Lagoon in the local reports and in the papers listing the winter severity and ice in Venice223. The reason is that the extreme cold occurred since the beginning of December, when the Adriatic Sea is not cold enough to reach the freezing point, its temperature being around 12°-14°C224. Therefore, the formation of ice is a good index of the winter severity in January and February, less in December.

138This event was carefully documented by Giuseppe Crestani225 who was an excellent climatologist and at that time in charge as a member of the Water Magistrate at Venice, and by Zanon,226 of the Patriarcale Observatory in Venice. Beginning from January, arctic air blew over Venice and some snow fell. A second heavy snowfall (i.e. 22 cm) occurred at the end of January and a third (7 cm), at mid February. The snow lasted till March 8th. The daily mean temperature was below 0°C till February 18th. The coldest day was February 12th, and the temperature ranged between -8.5° and -13 °C. On February 3rd, ice started to appear on the Lagoon borders and in some internal canals, while a cold Bora wind was blowing (-10 °C). On February 10th, 11th, 12th, 13th cold Bora blew again and the Lagoon and all the canals were frozen over. The thickness of the ice slab ranged between 15 and 20 cm. Ice began melting on February 18th and disappeared, on 24th. In the City the cold broke some lead pipes for the distribution of water, forming unexpected ice fountains from walls. The period was characterized by a meridian-type flow with blocking high pressure over Western Russia (Fig.6a). A low-pressure trough was extended over central Europe from Scandinavia to Italy, bringing extremely cold polar air. The deep depression over the Northern Adriatic Sea was fed by the release of sensible and latent heat from the relatively warm sea waters. In Venice the violent Bora wind blew cold air from East. The effect was snow and long-lasting severe cold.

139On February 1st it was snowing. There was arctic and polar air in the following days. The North-Eastern part of the Lagoon froze. On the 4th, people walked over the Lagoon near the estuary. On February 10th, snow fell over whole Italy; strong Bora blew at Venice; the temperature dropped, reaching -8°C. The ice melted between February 21st and 26th when the temperature became milder, and finally the snow turned into rain. The Lagoon was partially frozen.

140On January 5th heavy snow, i.e. 20 cm, fell in Venice, followed by a flow of arctic air and cold Bora wind blew. The temperature dropped, and the minimum reached -12°C on January 7th and 11th. The North-Eastern part of the Lagoon froze, and the bridge connecting Venice to Mestre constituted the border of the ice sheet. In some internal canals in Venice, ice slabs were floating. On January 12th, the ice extended between Punta Sabbioni, S. Erasmo, Burano, Torcello and Ca' Zane on the Eastern side of the Lagoon and the ice sheet supported people crossing the Lagoon from Cavallino to Altino, and a football derby. Over two thousands Lagoon birds, especially wild ducks and herons, and local fish as well froze. After January 14th the meteorological situation changed: the warm Sirocco wind caused a rise in temperature and a rainfall on the 16th melted the ice.

141In 2012 the pressure pattern was similar to that in 1929, with a blocking high pressure over Western Russia and Scandinavia, and a low-pressure trough crossing central Europe from Scandinavia to Italy. A low-pressure minimum oscillated around central Italy. This situation blew extremely cold polar air from North to North-East. The general circulation in Venice was locally reinforced by Bora Wind. The extreme cold over Europe is evident from the temperature pattern reported in Fig.6b. On February 5th the North-Eastern part of the Lagoon was frozen over, the bridge connecting Venice to Mestre was the border of the ice sheet. The canals of the City, including the Grand Canal, had floating ice slabs, transported from the North-Eastern sector by the tidal currents. The Lagoon was partially frozen and the winter was classified very severe.

142Visual arts used in this paper are composed of paintings, engravings, watercolours, ink drawings and photographs. Only one original and various copies are available for the famous winter 1709, some independent paintings and several engravings for 1788, one for 1791. Several pictures are available for the 1929 and later winters.

143The earliest views of the Lagoon frozen over were two etchings on copper plate by Vincenzo Coronelli (Fig.7a,b) 227 in a collection of etchings printed in 1709 and entitled “La Brenta". Copies are at the Querini-Stampalia Foundation and the Library of the Museum Correr. The first etching is entitled "The iced Lagoon facing Murano [island] in the year MDCCVIII [1708 More Veneto i.e. 1709 A.D.] and represents some people joking on ice. This etching is the first visual document, focused on some amusements during this exceptional event. An Anonymous reproduced this etching as oil on canvas, and the painting is exposed at the Querini-Stampalia Gallery. The legend reads: “On January 15th 1708 [More Veneto], this side of the Lagoon was frozen over. People could walk over for miles. This situation lasted for 10 days.” The second is entitled "The iced Lagoon facing Mestre [in the hinterland] in the year MDCCVIII" and represents some people transporting animals (pigs, sheep, chicken) and other supplies on ice. This particular view and the path to Mestre will inspire Francesco Battaglioli, Teodoro Viero, Giovan Battista Ersego, Francesco Guardi and Giacomo Guardi in the occasion of subsequent great winters, as we will see later. Other similar etchings and a painting by Gabriele Bella at the Correr Museum are dated 1708 [More Veneto] but very likely they were produced later 228 to take advantage of the market.

144The ice slab was impressive and the growing interest stimulated the Venice artists and some anonymous followers of their schools to produce various etchings and paintings, with a flourishing business. Just to give an idea, only the Museum Correr has one pen drawing, three oil on canvas and seven etchings on this subject. An oil on canvas made by an Anonymous follower of the school of Francesco Battaglioli, is dated 1788 [More Veneto?] and is kept at Ca’ Rezzonico.229 In this painting (Fig.8) the view is from San Giobbe, facing St. Second Island and Mestre, the same in the etching by Coronelli in Fig.7b. The legend in the scroll reads: “in 1788 [More Veneto?], the last month of the year [i.e. February 1789 A.D. if the legend was written More Veneto; alternatively December 1788 A.D. if the legend was written More Romano] ice started to form the 28th and lasted till the 10th of the next month [i.e. March 1789 A.D. if the legend was written More Veneto; alternativelyJanuary 1789 A.D. if the legend was written More Romano], when the transit between the two borders was interrupted. This painting will preserve memory of it”.230 From the above written documents we know that the extreme cold started at the end of December 1788 and ice on January 4th 1789 A.D. and the date is More Veneto.

145The oil on canvas at Ca’ Rezzonico and the other similar etchings are of extraordinary relevance for their content. They realistically show the situation, the long line of people with sleighs and food going from Venice to Mestre and vice-versa along the path shown in Fig.2 and the caravan with provisions to the City, already portrayed in Fig.3. It should be also noted that the ice sheet was thick on the Lagoon, North and East of Venice, but in the internal canals it was not thick enough to carry people and supplies. For this reason narrow channels were opened by breaking the ice to connect the safe ice area with the interior of the City and, to allow the distribution of supplies. Indeed, the painting shows an icebreaker boat with a workman hitting the ice with a hammer or an axe to allow the internal transport of food and supplies. Wooden planks are used to bridge the narrow channel of broken ice and to provide a safe path over thin ice. On the main ice slab some boats are used as sleighs.

146The above oil on canvas inspired in general, and in various details, a series of later paintings and it was reproduced in a number of etchings with some minor changes, that display funny popular amusements. For the reasons we will discuss later, nobody knows when originals and copies were made, and the Museum curators preferred to date in terms of century. All of these visual arts are useful for their content, not for their obscure chronology.

147An etching on copper by Teodoro Viero (Fig. 9) kept at the Correr Museum is characterized by the Dance of Moors. The Dance of Moors, also known as Moorish or Morris Dance depicting the struggle of the Moors and Christianity was very popular and widespread over Europe. The dance was based on rhythmic stepping and the execution of choreographed figures that constituted a pantomime of war. It was performed without music or particular songs; it simulated a battle, fighting or jumping around with real swords or imaginary weapons, following the Moor style. The dance formed wide circle, resembling a ring-around-a-rosy. The detail in Fig. 9b shows a number of dancers, maybe soldiers, forming a circle and duelling with swords.

(a) Etching by T. Viero at the Correr Museum, Venice. (b) Detail of the Dance of Moors, i.e. a pantomime of war where dancers depict the struggle of Moors and Christianity, fighting with swords.

Correr Museum, Venice, St. Gherro, 1670.

148The Strengths of Hercules consisted, typically, of two human pyramids facing each other. Each pyramid was formed by people from two main districts of the City in competition. In this paper we will shortly analyze three etchings with human pyramids, i.e. the xylography in Fig. 2, an etching by Giovan Battista Ersego (Fig. 10), kept at the State Archive, and another by Teodoro Viero (Fig. 11), also at the State Archive. The xylography and the two etchings display only one pyramid, probably because it was really very risky to build-up two pyramids at short distance on slippery ice. To be visible, the details of the Strengths of Hercules have been reported in Fig. 12.

Detail with human pyramids of the Strengths of Hercules: (a) Xylography in Fig.3 right side, with 7 men (3+2+1+1) pyramid. (b) Etching by G.B. Ersego in Fig.10, with 8 men (4+2+1+1) pyramid. (c) Etching by T. Viero in Fig. 11, with 16 men (8+4+2+1+1) pyramid

149The detail of the xylography in Fig. 12a (detail of Fig. 3)shows a human pyramid composed of seven men, i.e. three men forming the basis, plus an expert giving suggestions; on their shoulders two standing men, then another standing man and, finally, an upside-down topping person (Fig.12a). The pyramid is composed of four levels, with 3+2+1+1 men. The equilibrium was reached with feet leaned on shoulders, except for the topping man who stays head by head and hands by hands. The etching by Ersego (Fig. 12b) shows an eight men human pyramid of four levels, with 4+2+1+1 men, plus two controlling experts. This time the equilibrium has been reached with the help of poles for a better distribution of weight but especially they constitute a frame to resist to horizontal forces and tottering. The basis is composed of two pairs of men; each pair carries a pole on shoulders, forming a “V”. The two poles constitute the base for other two men forming another base with an additional pole that is oriented to form the horizontal bar of an “A” if one considers the projection of this pole and the “V”. The next two levels are both composed of only one man, one standing and one upside-down on the top. The etching by Viero (Fig. 12c) is impressive, being composed of 16 men, and follows a similar modular and framed structure, but bigger and with a further level, i.e. 8+4+2+1+1 type, plus the usual supervisor. The basis is composed of three pairs, with three poles, arranged either in “Y” or “Δ” form, which support the subsequent modules, as discussed above.

231See above note 105.

150The above Strength of Hercules may give an idea about the load bearing capacity of the ice. The pyramid composed of 8 men and 2 supervisors is equivalent to 700 kg distributed over 2 m2, but we should consider that there are some other people in close proximity. The load of the 16 men pyramid and a supervisor is around 1200 kg, which requires an ice thickness exceeding 40 cm considering that the load may be increased by onlookers and is associated with vibrations. This is realistic, especially if we consider that in 1755 the ice sheet reached 43 cm thickness, indicated by the above-mentioned documentation evidence.231 In addition, the etching shows that the 16 men pyramid has considered the problem of the huge load concentrated on the very small area of a few feet: for this reason a number of wooden planks has been placed on ice to create a wide basement and distribute weight. This clever and realistic solution suggests that the impressive pyramid was not invented by the painter. The above representations give an idea of the thickness of the ice slab carrying so many people and carriages and confirm the descriptions of documents.

232Morassi, 1975.

233Morassi, 1975.

151The Venetian painter Francesco Guardi (1712-1793), who was eyewitness, depicted an essential and elegant watercolour with a view similar to the oil on canvas in Ca’ Rezzonico and the above etchings. People are walking on ice, most of them in a precession manner, thinking they were following the safest and already tested path to reach the hinterland. Some others are carefully testing the ice strength in other points. The watercolour was sold to an Englishman and was in the collections of Malcom Bullock and Lady Irwin, London.232 The frame reports a legend: “in winter 1787 [More Veneto, i.e. 1788 A.D.] the Lagoon around Venice was frozen over...”. The date is surprising because the winter 1787-88 was normal to mild, while a great winter occurred in 1788 More Veneto, i.e. 1789 A.D.. The art historian Antonio Morassi233 suggested that in reality the watercolour refers to the winter 1788-89 and was the model for other two paints, with the same subject, made by Giacomo Guardi, son of Francesco (see later, winter 1791 and Fig. 13). We believe that the watercolour was made some years after the event, with artistic purposes, on request of a foreign client (i.e. unfamiliar with the local events), with the aim of showing a Venetian curiosity, but disregarding the exact chronology of harsh winters.

152An interesting gouache signed Francesco Guardi (Fig.12) is kept at the Correr Museum. It is almost identical to the watercolour dated 1787 and kept in London. This gouache may be related to another drawing made by Giacomo Guardi, also in London, at the Simonson Collection234. The bottom legend is “View of the Lagoon, from St Giobbe in front of St Secondo Island when the Lagoon is frozen over January 3rd, 1790 [More Veneto, i.e. 1791 A.D.]. Guardi F”. Although the signature indicates Francesco Guardi, the gouache should be attributed to Giacomo Guardi (1764‑1835), son of the famous Francesco.235 One should consider that at that time Francesco Guardi was 79-year old and died two years later. Giacomo had the practical conduction of the studio and preferred to sign with the name of the official master of the studio, i.e. Francesco, for the higher commercial evaluation of his prestigious name.

153The problem met with signatures is not new. It is well known 236 that the Venetian painter of vedutas Giovanni Antonio Canal (1697-1768) nicknamed Canaletto produced many paintings with the help of his studio assistants; one of them was his nephew Bernardo Bellotto (1721-1780). Bellotto was an excellent pupil and soon equalled his master and in 1738 was officially recognized as painter by the Venice painter association. However, in the period from 1738 to 1743 he continued to sign his paintings "Canaletto". The level reached by Bellotto and the ability in using the style of the Canaletto studio was so high that many art historians had difficulty in distinguishing early works of Bellotto from that of Canaletto. Some 55 views of Venice, that in the past were attributed to Canaletto, today are attributed to Bellotto237. The competition between the two painters practically obliged Bellotto to leave Venice in 1747, and move to Dresden, Vienna, Munich and Warsaw, where he died. However, even outside Venice, especially in Germany and Poland, Bellotto continued to call himself by his uncle's illustrious name Canaletto. It is not surprising that Francesco Guardi, who was a friend and colleague of Canaletto and Bellotto, made the same for business purpose, especially because this was the normal use.

238The six paintings are: two at the Fitzwilliam Museum, Cambridge; one in a private collection; one a (...)

154In the Venice craft tradition, a painter had to be officially recognized by the local official painter association. Once recognized, the painter could found a studio and become the "master of the brush" with a number of assistants and pupils that cooperated at various levels to the production of paintings. Only the master was authorized to sign the paintings and his signature had the meaning of registered trade-mark and determined the price, irrespectively of the personal contribution of the master. If a particular painting had success, the studio reproduced it a number of times to satisfy all requests. For instance, we know six identical paintings: "View of the Grand Canal: Santa Maria della Salute and the Dogana from Campo Santa Maria Zobenigo" by Canaletto or Bellotto238. The replicas were easily made by pupils, with little or no intervention of the master, but were in any case signed by the master, because the signature determined the commercial value of the paint.

239Segarizzi, 1910.

240Morassi, 1975.

241Morassi, 1975.

155Returning to the gouache by Giacomo Guardi, the date too is surprisingly misprint 239, or even "false". This can be established because no other evidence from written sources or from instrumental records has been found for ice: neither in January 1790 (i.e. the date as it is read in the legend) nor in January 1791 (i.e. as it should be interpreted because at that time all dates in Venice were More Veneto). Furthermore, the temperature record in Padua for that period reveals that the daily temperature never dropped below 0°C with the exception of only few days with average around -1 °C. This air temperature was not sufficient to freeze salt water, whose freezing point is -2 °C, and one should also consider that the tidal exchanges bring mild water into the Lagoon, as already discussed (section 4). Morassi 240 suggests that the two paints by Giacomo Guardi were inspired by the original watercolour dated 1787 and highly likely made a few years after the grand winter 1789 but before 1793, when Francesco died.. Another similar painting by Giacomo Guardi is at the G. Simonson Collection, London, but without legend, signature and date241. Wrapping up, Giacomo Guardi was simply interested to produce, and sell, some attractive gouaches, that substantially were a replica of the watercolour made by his father a few years after the frost. The conclusion is that paintings showing a Venetian curiosity, e.g. people walking on ice, were business artworks appreciated by the foreign market and cannot be used for dating purposes.

156Among the various pictures taken in 1929, we have selected the view of sailing boat frozen into the ice in the Lagoon between Venice and Saint Michael Island, on February 13th, 1929 (Zanon, 1929) (Fig. 14).

157The picture of a canal frozen over in February 1929 but with dangerous holes for the underlying warmer water current due to the tidal exchanges with the sea is shown in Fig.15a. Some snow is visible on the ice sheet and on the roofs. On the side of this picture, another has been reported, taken in 2012 with ice slabs floating on the water surface (Fig.15b). The difference is evident: in 1929 the winter was great (GW), with harder and thicker ice, forming an almost continuous sheet; in 2012 the winter was very severe (VS), with many floating ice slabs, 4 cm thick. In addition to the meteorological reasons i.e. less intense cold and for a shorter period, the excavation of new deep canals for tankers and cruise ships has increased the tidal exchanges making the formation of an ice sheet more difficult in comparison with the past centuries, as it has been discussed in section 4.

158So far we have seen that both the intensity of cold and its duration are fundamental factors to determine the formation of ice on the Lagoon. In this section we want to analyse the role of these two factors, deduced from instrumental records, and how they are related to harsh winters, i.e. GV and VS. To this aim we should introduce two parameters: the ice days and the freezing degree-days.

242Camuffo and Jones 2002; Camuffo and Bertolin 2012.

159An ice day (ID) is defined when the air temperature remains below the freezing point for the whole day, and represents a day in which ice never melts. From the instrumental records we have selected the ID and then computed their average temperature that has been reported per each year and each century (Fig. 16). This has been computed for the instrumental period when readings are available in Padua, i.e. from 1716 to 2012, with a minor gap from 1718 to 1725.242 The absence of dots from 1764 to 1773 is not a gap in information (regular daily readings were taken by Morgagni till 1768 when he died, and by Toaldo who started in 1766); but corresponds to a period of mild winters. In the same plot a red label is reported for the GW found in the written sources, and a blue label for the VS. Wrapping up, the 18th century had five GW and three VS winters; the 19th century only two VS; the 20th century one GW and two VS, and this century had one VS, despite the global warming. The top great winters were occurred in 1709, 1755, 1789 and 1929. The plot in Fig.16 shows how the events described in the sources match with the thermometer readings. The agreement is generally good, but not perfect, because the formation of ice in the Lagoon depends on a number of variables, as already discussed.

Average temperature of ice days in Venice. Red labels are for great winters in: 1709, 1740, 1755, 1758, 1789 and 1929; blue for very severe winters in: 1716, 1776, 1784, 1820, 1864, 1956, 1985 and 2012. Shading is for missing instrumental readings.

160Degree-days are defined as departures of air temperature from a given standard. Freezing degree-days (FDD) are computed as a cumulative departure below the freezing point, i.e. 0°C. The value may be accumulated (summed) over any period of time, depending on the aim. For instance, FDD = ∑(Ti – T0) is the sum over a month of the differences Ti – T0, whereTi is the average daily temperature (when it was below 0°C) and T0 = 0°C; the running label i runs from 1 to the highest number of ice days of the month. In practice, T0 = 0°C and FDD = ∑Ti.

161FDD is a measure of both duration and magnitude of below-freezing temperatures during a specified period. The FDD for a given month tells how cold it has been for how long. This index has been computed for the months of December, January and February of each year (Fig.17), as the monthly count of days in which the average temperature did not rise above the freezing point. It might be less representative of the occurrence of ice sheets in the Lagoon. However, when cold culminated around two consecutive months, the total count is partitioned between the two months, obscuring the related peaks. On the other hand, if the whole cold season is considered, the repeated occurrence of spurious short cold events might grow exceeding and obscuring great winter peaks. This should be kept in mind when reading the plots. However, the plot clearly shows that the most critical period is January, followed by a few sporadic but sharp peaks in February; finally December, but less relevant. The severity culminated in the 18th century, followed by the 19th and the 20th, in line with a general warming trend.

Freezing degree-days in Venice as cumulative departure below the freezing point, for the winter months December, January and February. Shading is for missing readings.

162The next plot (Fig. 18) combines the number of the ice-days (i.e. the number of days in which the average temperature was below 0 °C) with the freezing-degree-days (i.e. the sum of all degrees (below 0 °C) that have characterized the ice days). This constitutes a synthesis of the previous two figures, but loosing the temporal evolution, hereafter any trend. The three winter months have more or less the same distribution, except for the density of population. The plot suggests that the longest periods reach the lowest temperatures, although with some scattering and the problem that some cases falling around two months are consequently cut and partitioned between the two related months.

243Polar air starts very cold and dry but it may become milder passing over the relatively warm waters (...)

163The plots from the instrumental records show that very severe (VS) or great winters (GW) occur in Venice when the cold is very intense and lasts between two weeks and one month. The typical weather is formed by "blocking", i.e. large-scale patterns in the atmospheric pressure field that are nearly stationary, blocking the usual Westerlies and advection of moist and mild air from the Atlantic Ocean. Staying in the same position for weeks, this particular meteorological situation blows polar or arctic air243 and keeps cold weather for a long period of time, e. g one to three weeks. In winter, the most typical block is constituted of a high pressure over Western Russia or Scandinavia. This cold air will reach the Mediterranean blowing from North or from East. In Venice, this weather situation is locally associated with clear sky and Easterly Bora, that is a very cold and fresh to gale wind. This means that the Lagoon is rapidly cooled and ice may form when the intensity and duration of cold air spells will exceed the mitigation effect of the tidal exchanges.

Relationship between intensity and duration of cold periods, expressed in terms of freezing degree-days (i.e. the sum of all degrees below 0°C that have characterized the ice days) versus number of ice days (daily averages<0°C), for the three winter months during the instrumental period, with colour code divided by centuries

164This study demonstrates the importance of interdisciplinary approach to provide a clear image of the most severe winters in Venice, when the Lagoon was frozen. This paper used written documents, visual evidence and instrumental records. Beyond a climate series that deserves its own merit, the paper shows climate's ramifications on daily life of the society at Venice, and the citizens' efforts to save themselves from these difficult situations, without neglecting the opportunity for some unplanned amusement.

165The written sources provided a lot of direct or indirect information that has been essential especially before the instrumental period. The descriptions in the documents made possible a classification of winter severity, especially in the case of the harsh winters: very severe (VS) and great winters (GW). The classification was based on objective effects related to the ice extension and thickness, freezing of wine, wells, killed animals and trees etc. This required solving a number of problems, especially in the identification of the exact date, created by uncertain uses in the early mediaeval period, or the complex dating style in use in the various cities and changing over time. This complexity, misinterpretation or errors in copying early documents, or bad quotation of sources has caused duplications of events that required an accurate critical work to recognize the true events (or, at least, the most probable ones) from wrong duplicates. Not only the content of the documents was important, but the missing information too, especially to confirm or reject unclear cases. The validation of the data has been based on climatic, statistical and historical criterions. The common period of written documents and instrumental records (i.e. 1700-today) has been essential to refine the interpretation and the relationships between cold intensity, duration and visible effects.

166The visual arts have been also useful, but needed a special interpretation because they belong to a totally different dimension. Documents were written to inform, possibly in objective form, at no cost. Paintings were aimed to provide pleasant, artistic views and produced to be sold. Especially in the 18th century, paintings were made in studios, with various contributions of assistants and pupils under the supervision of the master who signed the artwork. If the subject was appreciated, the painting was reproduced. The business was especially flourishing for the numerous rich English noblemen who travelled to Venice during the first half of the eighteenth century for cultural aims and wanted to return with a charming memory/documentation: either oil on canvas, watercolour or etching, depending on price. This business produced many paintings with misleading signatures and dating. To our aims the visual arts provide unparalleled information about the iced Lagoon in the 18th century, to calculate the ice thickness, to know the path followed by Venetians to reach the hinterland, the transport of supplies, etc. They cannot be used, however, for dating purposes.

167The instrumental observations over the last three centuries provided further, objective evidence. In some cases the peak of cold of some great winters, such as in 1755 and in 1758 was exceeded by peaks of very severe winters of 1864 and 1985. The crucial factor for the formation of a thick ice sheet is that the cold air blowing from the polar region persists for a long time. The synergism between the various factors leading to the formation of the ice sheet on the Lagoon may induce a substantial difference in classifying winter severity by the written sources and visual arts, or in considering peaks of cold, i.e. the lowest temperature recorded within a certain period, or the averages carried over a certain duration of the instrumental record (e.g. day, week, month).

168A conclusion is that in general the above written and visual proxies and the instrumental records can be used to classify the winter severity, except when the extremely cold air blows at the beginning of December, as in 1879, because the sea temperature is too high for ice. However, not always the classes of winter severity based on proxies can be easily transformed and expressed in terms of instrumental readings because the same effect (e.g. ice thickness) may be obtained with different combinations of cold intensity and time duration.

244Like any subdivision by classes or in time intervals, the subdivision by centuries and the secular (...)

169The analysis of the written and visual proxies and the instrumental readings points to the meteorological situation that is responsible for these events. Typically, this is a block generated by a high-pressure over Western Russia or Scandinavia that brings arctic or polar air to Venice, and lasts for weeks and sometimes reaching a month. The last three centuries have been characterized by the transition from the Little Ice Age to the Global Warming; over this period the number of occurrences of extreme winters is decreasing. Over the last millennium the mean occurrence of great winters was two or three per century244 (i.e. 2 GW/century in 12th, 13th and 17th century; 3 GW/century in 14th, 15th and 16th century). The peak of occurrence was in the 18th century with 5 GW; the minimum was in the 19th century with no GW, followed by the 20th century with only one.

170In this research, science, history and art have been applied to reconstruct the past climate in Venice, extreme events and trends. Culture has been found to have two complementary aspects that provide a nice example of positive synergism. On one hand, science is finalized to preserve mankind, his culture and the environment. On the other hand, culture provides science with the basic knowledge and with the necessary input in form of proxy data generated from literature and visual arts.

COTTE, L., 1790: The effects of the cold of the winter 1788-89 on animals and vegetables. Lecture note read by P. Cotte in the Royal Society of Agriculture in Lion, September 5, 1789. The Edinburgh Magazine or Literary Miscellany. Vol. XII, Dec. 1790, pp 400-402

Notes

1The Exarchate of Ravenna was a centre of Byzantine (East Roman) power in Italy, from the end of the 6th century to 751.

2After the treatise of Campoformido, October 17th 1797, Venice and Milan were assigned to France. Napoleon Bonaparte was crowned the King of Italy on May 26th 1805. Milano was the capital of this kingdom and a number of Venetian artworks and documents were moved to Paris and Milan.

3The "kingdom" of the Lombardy and Venetian regions was formally instituted with the Congress of Vienna (November 1st 1814 — June 8th 1815). A number of Venetian artworks and documents were moved to Vienna and Milan.

7The State Archive was founded in 1815 with the name: Archivio Generale Veneto (i.e. General Archive of the Venice region). When Venice joined the unified reign of Italy in 1866, it became State Archive.

20Tho Hexapolis exist. The Doric Hexapolis was a federation of Greek city-states in South-Western Asia Minor (i.e. Kos, Cnidus, Halicarnassus, Lindus, Ialysos and Camirus) founded by Doric colonist; the Armenian Hexapolis was a group of six cities in Armenia Minor located on the road between Cappadocian Caesarea and Melitene. The frequent use of Greek words, written in Greek alphabet suggests that Fritsche was Greek; at the end of his dedication to Prince Ferdinand, after his signature he added that he was living in High Lusatia, i.e. a region on North East Germany, near Silesia.

38The Julian Calendar introduced by Julius Caesar in 46 BC was the predominant calendar in the Roman world, most of Europe and elsewhere, until it was refined and gradually replaced by the Gregorian Calendar, i.e. the modern dating style, promulgated by Pope Gregory XIII in October 1582. The Julian Calendar started from the 1st January and the length of the year was 365.25 days; the Gregorian Calendar had the same starting day but refined the year length to 365.2425 days.

40More exactly, they respectively are 2/100 and (2/100) × (1/99) = 1/4950 = 0.00020202.... Note: The above evaluation has been made under the hypothesis of a stationary system; as the climate system is slightly variable, the calculation should improved; however we have preferred to refer to the simplest and easiest approach to giving a general idea about the problem.

41Proxy data are natural or man-made indicators that preserved physical characteristics of the environment and can stand in for direct measurements.

42Siltation is the fine particulate terrestrial clastic material transported in suspension by the turbulent water of rivers; when this material enters the Lagoon and finds still water, it sediments on the bottom.

49When a thick cloud cover is present, it intercepts and returns back a large part of the IR radiation (i.e. net flux balance tending to zero); in the case the atmosphere is dry and the sky is clear, most of the IR escapes from the atmosphere (i.e. negative net flux balance) with intense soil cooling.

50The solar income is the amount of solar energy that falls on a surface (e.g. the Lagoon) as sunlight.

52The largest tidal cycles occur when the Earth, the Sun and the Moon are in conjunction (new Moon) or opposition (full Moon). This astronomical alignment of Sun, Moon and Earth is called syzygy.

53The cumulative effect is additive, being equal to the sum of (small) separate (e.g. day-by-day) effects (e.g. the net heat loss), but summed over long time periods. This holds for physical entities that have a long-term memory. The Lagoon, for its exchanges with the Sea, has a short memory of the past weather conditions.

196Invented by Guillaume Amontons in 1702 is the first air thermometer, used in association with a barometer. The thermometer had an air pocket compressed by a column of mercury having the tube open on the top, and was sensitive to the atmospheric pressure. The readings were corrected adding the height of the mercury column read in the barometer.

238The six paintings are: two at the Fitzwilliam Museum, Cambridge; one in a private collection; one at Getty Museum, Malibu (Los Angeles); one was at the Stewart Collection and was sold by Christies'; another by Anonymous is at Ca' Rezzonico.

243Polar air starts very cold and dry but it may become milder passing over the relatively warm waters of the North Atlantic (maritime Polar) or may remain very cold if it follows a path over Scandinavia, Eastern Europe and Russia (continental Polar). Arctic air has similar characteristics to a Polar air but, because of the different sea track it may reach the Mediterranean area colder than a maritime Polar, or milder than a continental Polar. However, either Arctic or Polar, very cold and dry air blows from North.

244Like any subdivision by classes or in time intervals, the subdivision by centuries and the secular counting is arbitrary for the particular choice of the starting and ending dates; however, this is a useful reference.

List of illustrations

Title

Fig. 1

Caption

Upper row: Percentage of the number of solar and lunar eclipses recovered with other natural events in our Data Bank (year 2000) in comparison with the total number of eclipses occurred in the same period (i.e. century by century), and known after astronomical calculations. Lower row: Number of primary and secondary sources that have been consulted. For symbols A, B, C, see comments in the text.

Path over the frozen Lagoon frozen from Fondamenta San Giobbe in Venice to Mestre in the hinterland, through S. Secondo Island (yellow arrow); the second path is from the Fondamenta Nuove passing on the side of Saint Michael Island and across Murano Island (red arrow).

Credits

Arrows have been applied to a xylography by Jacopo De’ Barbari (16th century, Correr Museum) with a realistic aerial view of Venice and its Lagoon. Correr Museum, Venice, inv. Cl XLIV n. 57)

Threshold for ice-bearing capacity, i.e. load limit versus ice sheet thickness. The threshold is the black line; the safe area is on the right side, shaded, except for a band close to the threshold limit.

Detail with human pyramids of the Strengths of Hercules: (a) Xylography in Fig.3 right side, with 7 men (3+2+1+1) pyramid. (b) Etching by G.B. Ersego in Fig.10, with 8 men (4+2+1+1) pyramid. (c) Etching by T. Viero in Fig. 11, with 16 men (8+4+2+1+1) pyramid

Relationship between intensity and duration of cold periods, expressed in terms of freezing degree-days (i.e. the sum of all degrees below 0°C that have characterized the ice days) versus number of ice days (daily averages<0°C), for the three winter months during the instrumental period, with colour code divided by centuries